U.S. patent application number 14/342012 was filed with the patent office on 2014-11-13 for pure metal and ceramic nanofibers.
This patent application is currently assigned to CORNELL UNIVERSITY. The applicant listed for this patent is Daehwan Cho, Nathaniel S. Hansen, Yong Lak Joo. Invention is credited to Daehwan Cho, Nathaniel S. Hansen, Yong Lak Joo.
Application Number | 20140332733 14/342012 |
Document ID | / |
Family ID | 47756865 |
Filed Date | 2014-11-13 |
United States Patent
Application |
20140332733 |
Kind Code |
A1 |
Joo; Yong Lak ; et
al. |
November 13, 2014 |
PURE METAL AND CERAMIC NANOFIBERS
Abstract
Provided herein are nanofibers and processes of preparing
nanofibers. In some instances, the nanofibers are metal and/or
ceramic nanofibers. In some embodiments, the nanofibers are high
quality, high performance nanofibers, highly coherent nanofibers,
highly continuous nanofibers, or the like. In some embodiments, the
nanofibers have increased coherence, increased length, few voids
and/or defects, and/or other advantageous characteristics. In some
instances, the nanofibers are produced by electrospinning a fluid
stock having a high loading of nanofiber precursor in the fluid
stock. In some instances, the fluid stock comprises well mixed
and/or uniformly distributed precursor in the fluid stock. In some
instances, the fluid stock is converted into a nanofiber comprising
few voids, few defects, long or tunable length, and the like.
Inventors: |
Joo; Yong Lak; (Ithaca,
NY) ; Hansen; Nathaniel S.; (Ithaca, NY) ;
Cho; Daehwan; (Ithaca, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Joo; Yong Lak
Hansen; Nathaniel S.
Cho; Daehwan |
Ithaca
Ithaca
Ithaca |
NY
NY
NY |
US
US
US |
|
|
Assignee: |
CORNELL UNIVERSITY
ITHACA
NY
|
Family ID: |
47756865 |
Appl. No.: |
14/342012 |
Filed: |
August 30, 2012 |
PCT Filed: |
August 30, 2012 |
PCT NO: |
PCT/US12/53097 |
371 Date: |
June 9, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61528895 |
Aug 30, 2011 |
|
|
|
61636095 |
Apr 20, 2012 |
|
|
|
Current U.S.
Class: |
252/513 ;
252/514; 252/519.5; 252/520.1; 264/465; 420/441; 420/469; 420/501;
420/525; 420/563; 420/8; 423/594.18; 423/594.19; 423/600; 423/604;
423/608; 423/622; 75/345 |
Current CPC
Class: |
C04B 2235/444 20130101;
C04B 2235/526 20130101; C04B 2235/443 20130101; D01D 5/0015
20130101; H01B 1/026 20130101; A61K 31/202 20130101; C04B 35/62259
20130101; B22F 9/30 20130101; C04B 2235/449 20130101; D01F 1/10
20130101; D04H 1/728 20130101; H01B 1/02 20130101; H01B 1/08
20130101; C04B 35/6224 20130101; C04B 2235/441 20130101; B82Y 30/00
20130101; B22F 1/0025 20130101; D04H 1/4234 20130101; C04B 35/6225
20130101; C04B 2235/5296 20130101; C04B 35/62236 20130101; D01F
9/08 20130101; C04B 35/62231 20130101; C04B 35/62254 20130101; C04B
2235/40 20130101; C04B 2235/5264 20130101; A61K 31/232 20130101;
C04B 35/62227 20130101; B22F 1/0044 20130101; D01D 5/0007
20130101 |
Class at
Publication: |
252/513 ;
264/465; 423/594.19; 423/604; 423/622; 423/594.18; 423/608;
423/600; 252/514; 252/520.1; 252/519.5; 75/345; 420/441; 420/469;
420/501; 420/8; 420/525; 420/563 |
International
Class: |
D01D 5/00 20060101
D01D005/00; B22F 1/00 20060101 B22F001/00; H01B 1/02 20060101
H01B001/02; D01F 1/10 20060101 D01F001/10; H01B 1/08 20060101
H01B001/08 |
Claims
1-79. (canceled)
80. A process for producing one or more nanofiber, the process
comprising electrospinning a fluid stock, the fluid stock
comprising metal precursor(s) and polymer, the weight to weight
ratio of the precursor(s) to polymer being at least 1:2; and the
fluid stock being aqueous.
81. The process of claim 80, wherein the fluid stock is co-axially
electrospun with a gas.
82. The process of claim 81, wherein the gas is a high-speed
gas.
83. The process of claim 82, wherein the high speed gas is high
speed air having a velocity of about 100 m/s.
84. The process of claim 81, wherein the weight-to-weight ratio of
the precursor(s) to polymer is at least 1:1.
85. The process of claim 84, wherein the weight-to-weight ratio of
the precursor(s) to polymer is at least 1.5:1.
86. The process of claim 84, wherein the weight-to-weight ratio of
the precursor(s) to polymer is at least 2:1.
87. The process of claim 81, wherein one or more of the
precursor(s) are present in the fluid stock in a polymer-precursor
association.
88. The process of claim 87, wherein at least 25% of the polymer is
saturated with precursor molecules.
89. The process of claim 81, wherein the precursor(s) is present in
the fluid stock in a concentration of at least 200 mM.
90. The process of claim 89, wherein the precursor(s) is present in
the fluid stock in a concentration of at least 250 mM.
91. The process of claim 90, wherein the precursor(s) is present in
the fluid stock in a concentration of at least 300 mM.
92. The process of claim 81, wherein the metal precursor comprises
Ag, Cu, Ni, Fe, Co, Pb, Au, Sn, Al, Zr, Li, Mn, Cr, Be, Cd, Si, Ti,
V, Hf, Sr, Ba, Ge, or combinations thereof.
93. The process of claim 81, wherein the metal precursor comprises
one or more metal acetate, metal nitrate, metal chloride, metal
methoxide, or a combination thereof.
94. The process of claim 81, wherein the polymer is polyvinyl
alcohol (PVA), polyvinyl acetate (PVAc), polyethylene oxide (PEO),
polyvinyl ether, polyvinyl pyrrolidone, polyglycolic acid,
hydroxyethylcellulose (HEC), ethylcellulose, cellulose ethers,
polyacrylic acid, polyisocyanate, or a combination thereof.
95. The process of claim 81, wherein the metal precursor comprises
metal acetate and the polymer comprises polyvinyl alcohol
(PVA).
96. The process of claim 81, further comprising calcining the
electrospun material.
97. The process of claim 96, wherein the calcining of the
electrospun material comprises thermally treating the electrospun
material, chemically treating the electrospun material, or
both.
98. The process of claim 97, wherein thermally treating the
electrospun material comprises heating the electrospun material to
at least 400.degree. C.
99. The process of claim 97, wherein chemically treating the
electrospun material comprises treating the electrospun material
with oxygen.
100. The process of claim 97, wherein calcining the electrospun
material comprises heating the electrospun material to at least
400.degree. C. and treating the electrospun material with
oxygen.
101. The process of claim 96, wherein calcining the electrospun
material comprises removing polymer from the electrospun material
and converting metal precursor to metal, metal oxide, and/or
ceramic.
102. A nanofiber prepared according to a process of claim 81 and
comprising a continuous matrix of metal, metal alloy, metal oxide,
or ceramic.
103. A nanofiber prepared according to a process claim 81 and
comprising metal precursor(s) and polymer.
104. A nanofiber comprising metal precursor(s) and polymer, the
weight to weight ratio of the precursor(s) to polymer being at
least 1.5:1.
Description
CROSS-REFERENCE
[0001] This application claims the benefit of U.S. Provisional
Application Nos. 61/528,895, filed Aug. 30, 2011, and 61/636,095,
filed Apr. 20, 2012, both of which are incorporated herein by
reference in their entireties.
BACKGROUND OF THE INVENTION
[0002] Ceramic and metallic nanofibers have potential for
applications in a wide variety of fields, including high
performance filtration, chemical sensing, biomedical engineering
and renewable energy. Previous methods for producing ceramic or
metallic nanofibers include the electrospinning of sol-gel
precursors with or without a polymer binder. However, the
nanofibers produced by the sol-gel method have many disadvantages,
such as low performance and poor coherence, which makes them
unsuitable for many applications.
SUMMARY OF THE INVENTION
[0003] Provided herein are nanofibers and processes for producing
nanofibers. In some instances, the nanofibers are metal, metal
oxide, and/or ceramic nanofibers. In some embodiments, the
nanofibers are high quality nanofibers, high performance
nanofibers, highly coherent nanofibers, highly continuous
nanofibers, or the like. In some embodiments, the nanofibers are
coherent, are long, have few voids and/or defects, and/or have
other advantageous characteristics such as flexible control of
metal and/or ceramic crystal sizes. In some instances, the
nanofibers are produced by electrospinning a fluid stock comprising
a high concentration of ceramic or metal precursor in the fluid
feed stock. In some instances, the fluid stock further comprises
well mixed or substantially uniformly distributed precursor in the
fluid stock. In some embodiments, the fluid stock is converted to a
nanofiber comprising few voids, few defects, long or tunable
lengths, and the like.
[0004] Provided in certain embodiments herein is a process for
producing one or more nanofiber, the process comprising
electrospinning a fluid stock, the fluid stock comprising metal
precursor(s) and polymer, and [0005] a. the weight to weight ratio
of the precursor(s) to polymer being at least 1:2; [0006] b. the
fluid stock being aqueous; [0007] c. the precursor(s) being present
in the fluid stock in a concentration of at least 200 mM; or [0008]
d. any combination thereof.
[0009] In specific embodiments, the fluid stock is (1) a solution;
(2) a substantially uniform dispersion (e.g., of the precursor(s));
or (3) a substantially homogenous dispersion (e.g., homogeneous
dispersion of the precursor(s)). In further or alternative
embodiments, the weight-to-weight ratio of the precursor(s) to
polymer in the fluid stock is at least 1:2 (e.g., over 1:2) and the
fluid stock is aqueous. In specific embodiments, the
weight-to-weight ratio of the precursor(s) to polymer is at least
1:1. In further or alternative embodiments, the fluid stock is
prepared by combining reagent precursor(s), reagent polymer(s) and
water to form the fluid stock comprising the precursor(s) and the
polymer, and wherein the reagent precursor(s) and reagent
polymer(s) are combined in a weight to weight ratio of over 1:2. In
specific embodiments, the reagent precursor(s) and reagent
polymer(s) are combined the in a weight-to-weight ratio of at least
1:1. In further or alternative embodiments, one or more of the
precursor(s) are present in the fluid stock in a polymer-precursor
association. In specific embodiments, at least 50% of the polymer
is saturated with precursor molecules. In further or alternative
embodiments, at least 50% of the precursor molecules are associated
with polymer. In further or alternative embodiments, the
precursor(s) is present in the fluid stock in a concentration of at
least 200 mM (e.g., over 200 mM, at least 250 mM, or the like). In
specific embodiments, the precursor(s) concentration in the fluid
stock is at least 250 mM. In more specific embodiments, the
precursor(s) concentration in the fluid stock is at least 300 mM.
In further or alternative embodiments, the metal precursor(s)
comprises one or more metal-ligand complex. In specific
embodiments, the metal-ligand complex is in association with the
polymer. In further or alternative embodiments, the metal precursor
comprises metal selected from the group consisting of: Ag, Cu, Ni,
Fe, Co, Pb, Au, Sn, Al, Zr, Li, Mn, Cr, Be, Cd, Si, Ti, V, Hf, Sr,
Ba, Ge, and combinations thereof. In further or alternative
embodiments, the metal precursor comprises a transition metal, or
metalloid. In further or alternative embodiments, the metal
precursor is a metal-ligand complex comprising one or more ligand
selected from the group consisting of: a carboxylate, a nitrate, a
halide, a diketone, an alkoxide, and combinations thereof. In
further or alternative embodiments, the reagent precursor, the
precursor of the fluid stock, or both comprise one or more metal
acetate, metal nitrate, metal chloride, metal methoxide, or a
combination thereof. In further or alternative embodiments, the
polymer is polyvinyl alcohol (PVA), polyvinyl acetate (PVAc),
polyethylene oxide (PEO), polyvinyl ether, polyvinyl pyrrolidone,
polyglycolic acid, hydroxyethylcellulose (HEC), ethylcellulose,
cellulose ethers, polyacrylic acid, polyisocyanate, or a
combination thereof. In further or alternative embodiments, the
polymer is (i) hydrophilic, and (ii) water soluble or water
swellable. In further or alternative embodiments, the polymer is
thermally and/or chemically degradable. In further or alternative
embodiments, the polymer is a polymer comprising a plurality of
nucleophilic moieties and the reagent precursor is electrophilic.
In other embodiments, the polymer is a polymer comprising a
plurality of electrophilic moieties and the reagent precursor is
nucleophilic. In some embodiments, electrospinning the fluid stock
results in the formation of electrospun nanofiber material
comprising metal precursor and polymer. In further or alternative
embodiments, the process further comprises treating (calcining) the
electrospun material to prepare a calcinated nanofiber. In specific
embodiments, the treatment (calcining) of the electrospun material
comprises thermally treating the electrospun material, chemically
treating the electrospun material, or both. In further or
alternative embodiments, the process further comprises removing
(e.g., by calcination) polymer from the electrospun material. In
specific embodiments, calcining the electrospun material (e.g.,
under inert or reducing conditions) converts metal precursor to
metal. In further or alternative embodiments, calcining the
electrospun material (e.g., under oxidative conditions) converts
metal precursor to metal oxide. In further or alternative
embodiments, calcining the electrospun material (e.g., under
oxidative conditions) converts metal precursor to ceramic. In
further or alternative embodiments, calcining the electrospun
material (e.g., first under oxidative conditions and subsequently
under reducing conditions) converts a first metal precursor to
ceramic and a second metal precursor to metal. In further or
alternative embodiments, the process comprises calcining the
electrospun material under oxidative conditions, thereby converting
metal precursor to metal oxide (e.g., ceramic metal oxide). In
further or alternative embodiments, the process comprises calcining
electrospun material the nanofiber under inert or reducing
conditions, thereby converting metal precursor to metal. In further
or alternative embodiments, calcining the electrospun material
comprises heating the electrospun material to a temperature of at
least 400.degree. C. (e.g., at least 500.degree. C. or at least
600.degree. C.). In further or alternative embodiments, the fluid
stock is co-axially electrospun with a second fluid. In specific
embodiments, the second fluid is a gas (e.g., air). In other
specific embodiments, the second fluid is a second fluid stock
comprising a second metal precursor and a second polymer, wherein
the metal precursor and second metal precursor are the same or
different and the polymer and second polymer are the same or
different, and wherein the process produces a layered nanofiber
(optionally comprising coaxially electrospinning with a third fluid
that is a gas, e.g., air). In further or alternative embodiments,
the metal precursor and polymer being present (in the fluid stock
or precursor nanofiber) in a weight-to-weight ratio of at least 1:2
(e.g., at least 1:1). In further or alternative embodiments,
provided herein is a nanofiber prepared according to any process
described herein. In some embodiments, provided herein is a
nanofiber prepared by or preparable by any process described
herein. In specific embodiments, the nanofiber is a precursor or
electrospun nanofiber prepared or preparable prior to calcination.
In other specific embodiments, the nanofiber is a metal, metal
oxide, or ceramic containing nanofiber prepared or preparable
following calcination.
[0010] In some embodiments, provided herein is a precursor
nanofiber comprising polymer (e.g., organic polymer and metal
precursor. In some embodiments, the precursor nanofiber has high
metal precursor loading (e.g., at least 1:2, metal
precursor:polymer; over 1:2; at least 1:1.75; at least 1:1.5; at
least 1:1; or the like). In some embodiments, the precursor (i.e.,
electrospun) nanofiber (e.g., as prepared according to any process
described herein), comprises at least 90% by weight of organic
polymer and metal precursor. In further or alternative embodiments,
the precursor (i.e., electrospun) nanofiber comprises at least 5
elemental wt. % metal (e.g., at least 10 elemental wt. %, or at
least 15 elemental wt. % metal).
[0011] In certain embodiments, provided herein is a nanofiber or
plurality of nanofibers comprising metal, metal oxide, ceramic, or
a combination thereof, and: [0012] a. the nanofibers are at least
50 .mu.m (e.g., at least 100 .mu.m) long (e.g., on average); [0013]
b. the nanofibers have an (e.g., average) aspect ratio of at least
about 10 (e.g., at least about 100); [0014] c. the nanofibers
comprise a continuous matrix of a metal, a metal oxide, ceramic, or
a combination thereof (e.g., the continuous matrix running along,
e.g., on average, at least 80% of the length of the nanofiber; or
at least 90% the length of the nanofiber; or at least 95% the
length of the nanofiber); [0015] d. the nanofibers have an average
specific surface area between 1 m.sup.2/g and about 1000 m.sup.2/g;
or [0016] e. a combination thereof.
[0017] In specific embodiments, the nanofibers have feature (a). In
further or alternative embodiments, the nanofibers have feature
(b). In further or alternative embodiments, the nanofibers have
feature (c). In further or alternative embodiments, the nanofibers
have feature (d). In specific embodiments, the nanofibers have
features (a) and (b). In other specific embodiments, the nanofibers
have features (b) and (c). In still other embodiments, the
nanofibers have features (a), (b) and (c). In some embodiments, the
nanofibers comprise at least 33% (w/w) (e.g., on average) of a
metal, a metal oxide, a ceramic, or, taken together, a combination
thereof. In further or alternative embodiments, the nanofibers are
metal nanofibers comprising at least 90 elemental wt. % of metal
(e.g., on average). In further or alternative embodiments, the
nanofibers are metal oxide nanofibers comprising at least 90% metal
oxide (e.g., on average) and at least 30 elemental wt. % of metal
(e.g., on average). In further or alternative embodiments, the
nanofibers are ceramic nanofibers comprising at least 90% ceramic
(e.g., on average) and at least 30 elemental wt. % of metal (e.g.,
on average). In further or alternative embodiments, the nanofibers
are metal alloy nanofibers comprising at least 90% metal alloy
(e.g., on average) and at least 30 elemental wt. % of metal (e.g.,
on average). In further or alternative embodiments, the nanofibers
are composite nanofibers comprising a first material and a second
material, the first material being a continuous matrix material,
and one or both of the first material or second material comprising
metal, metal oxide, ceramic, or a combination thereof. In further
or alternative embodiments, the second material is a second
continuous matrix material (e.g., the first and second continuous
matrix materials are coaxial layers). In other embodiments, the
second material comprises isolated domains of the nanofibers. In
further or alternative embodiments, one or both of the first or
second materials comprises metal and the nanofibers comprising an
average of at least 5 elemental wt. % of metal (e.g., at least 20
elemental wt. % of metal) (e.g., on average). In further or
alternative embodiments, the first material is ceramic and the
second material is metal. In alternative embodiments, the first
material is metal and the second material is metal. In alternative
embodiments, the first material is ceramic and the second material
is ceramic. In further or alternative embodiments, the nanofiber
comprises at least 30 elemental wt. % of metal (e.g., on average).
In specific embodiments, the nanofibers comprises at least 50
elemental wt. % of metal (e.g., on average). In further or
alternative embodiments, the metal (of the metal, metal oxide,
ceramic, or the like) is selected from the group consisting of Ag,
Cu, Ni, Fe, Co, Pb, Au, Sn, Al, and combinations thereof. In
specific embodiments, the metal component comprises a ceramic or
metal oxide selected from the group consisting of Al.sub.2O.sub.3,
ZrO.sub.2, Fe.sub.2O.sub.3, CuO, NiO, ZnO, CdO, C, Ge, Si,
SiO.sub.2, TiO.sub.2, V.sub.2O.sub.5, VO.sub.2, Fe.sub.3O.sub.4,
SnO, SnO.sub.2, CoO, CoO.sub.2, Co.sub.3O.sub.4, HfO.sub.2,
BaTiO.sub.3, SrTiO.sub.3, and BaSrTiO.sub.3. In further or
alternative embodiments, the nanofibers comprise a metal-non-metal
alloy. In further or alternative embodiments, the nanofibers
comprise a conductive material, wherein the nanofibers have a
conductivity of at least about 10% (e.g., on average) when compared
with the conductivity of the conductive material when formed into a
sheet. In further or alternative embodiments, the nanofibers
comprise a continuous matrix of amorphous ceramic and comprise an
ultimate strength-to-diameter ratio of at least 0.075 MPa/nm (e.g.,
on average); a Young's modulus-to-diameter ratio of at least 0.15
GPa/nm (e.g., on average); and a fracture toughness of at least 0.6
MPA MPam.sup.1/2 (e.g., on average). In further or alternative
embodiments, the nanofibers comprise a continuous matrix of
amorphous ceramic and comprise an ultimate strength-to-diameter
ratio of at least 0.15 MPa/nm (e.g., on average); an Young's
modulus-to-diameter ratio of at least 0.3 GPa/nm (e.g., on
average); and a fracture toughness of at least 0.7 MPam.sup.1/2
(e.g., on average). In some embodiments, the nanofibers comprise a
continuous matrix of crystalline ceramic and comprise an ultimate
strength-to-diameter ratio of at least 5 MPa/nm (e.g., on average);
and a Young's modulus-to-diameter ratio of at least 1.5 GPa/nm
(e.g., on average). In some embodiments, the nanofibers comprise a
continuous matrix of crystalline ceramic and comprise an ultimate
strength-to-diameter ratio of at least 12.5 MPa/nm (e.g., on
average) and a Young's modulus-to-diameter ratio of at least 4
GPa/nm (e.g., on average). In further or alternative embodiments,
the nanofibers have a fracture toughness of at least 1.8
MPam.sup.1/2 (e.g., on average). In some embodiments, the
nanofibers comprise a continuous matrix of metal and have an
ultimate strength-to-diameter ratio of at least 0.35 MPa/nm (e.g.,
on average) and a Young's modulus-to-diameter ratio of at least 1.1
GPa/nm (e.g., on average). In some embodiments, the nanofibers
comprise a continuous matrix of metal and have an ultimate
strength-to-diameter ratio of at least 0.9 MPa/nm (e.g., on
average) and a Young's modulus-to-diameter ratio of at least 2.9
GPa/nm (e.g., on average). In further or alternative embodiments,
the nanofibers have an fracture toughness of at least 3.5
MPam.sup.1/2(e.g., on average). In further or alternative
embodiments, the nanofibers have a log(S/m) to log(S/m) ratio with
an identical bulk material of at least 0.8 (e.g., at least 0.9)
(e.g., on average). In further or alternative embodiments, the
nanofibers have a length of at least 50 microns (e.g., on average).
In further or alternative embodiments, the nanofibers have a
diameter of 500 nm or less (e.g., on average). In further or
alternative embodiments, the nanofibers have an aspect ratio of at
least 1000 (e.g., on average). In further or alternative
embodiments, the nanofibers comprise less than 5% (e.g., less than
3%, or less than 1%) carbon by elemental mass (e.g., on average).
In further or alternative embodiments, the nanofibers have (e.g.,
on average) less than 100 defects (e.g., less than 50, less than
10, or less than 5) per linear mm of nanofiber.
[0018] In some embodiments, the nanofibers described herein are
used in a sensor, a battery, a fuel cell, a solar cell,
ultracapacitor, catalyst, membrane, or electrode.
[0019] Described herein are hybrid nanofibers including hollow
nanofibers and multi-axial nanofibers comprising more than one
material. Provided herein are high quality nanofibers and processes
of preparing high quality nanofibers that are suitable for
applications such as electrochemical devices (e.g., batteries and
solar cells), advanced filtration, catalysis, and the like. In some
instances, the nanofibers provided and/or prepared according the
processes described herein are prepared at costs low enough to be
commercially viable. The present disclosure includes hybrid and
hollow nanofibers, use of nanofibers in many types of applications,
devices incorporating nanofibers, the use of devices incorporating
nanofibers, and the like.
[0020] In one aspect, described herein is a process for producing a
nanofiber. In some embodiments, the process includes
electrospinning a fluid stock. The fluid stock comprises metal
and/or ceramic precursor and polymer. In one embodiment, the weight
to weight ratio of the precursor to polymer is at least 1:2. In
some embodiments, the polymer is water soluble.
[0021] In another aspect, described herein is a process for
producing nanofibers, the process comprising electrospinning a
fluid stock, the fluid stock comprising metal precursor(s) and
polymer. In some embodiments, the fluid stock is (1) a solution;
(2) a substantially uniform dispersion (e.g., of the precursor(s));
or (3) a substantially homogenous dispersion (e.g., of the
precursor(s)).
[0022] In one aspect, described herein is a method for producing a
nanofiber, the method comprising electrospinning a first fluid with
a second fluid, at least one of the first or second fluids being an
aqueous fluid. In some embodiments, the first and second fluids are
electrospun about the same or similar axis. In some embodiments,
the first fluid is an aqueous fluid comprising water, a water
soluble polymer, and metal precursor. In some embodiments, the
second fluid is a second aqueous fluid, comprising water, a water
soluble polymer, and a second metal and/or ceramic precursor,
wherein the water soluble polymer of the second fluid is the same
or different than the water soluble polymer of the first fluid.
[0023] In one aspect, described herein is a method for producing a
nanofiber, the method comprising multi-axially electrospinning an
aqueous fluid stock and a second fluid. In some embodiments, the
aqueous fluid stock comprises water, a water soluble polymer, and
metal and/or ceramic precursor. In some embodiments, the second
fluid is a second aqueous fluid stock. In some embodiments, the
second fluid is a gas. In some embodiments, the second fluid at
least partially surrounds the aqueous fluid stock. In some
embodiments, the aqueous fluid stock at least partially surrounds
the second fluid.
[0024] In one aspect, described herein is a process for producing a
nanofiber, the process comprising electrospinning a fluid stock
comprising metal precursor, ceramic precursor, or combination
thereof wherein: (a) the fluid stock is aqueous; (b) the
concentration of the precursor in the fluid stock is at least 200
mM; or both (a) and (b).
[0025] In some embodiments, the fluid stock further comprises a
water-soluble polymer. In some embodiments, the precursor binds to
the water-soluble polymer. In some embodiments, the electrospinning
step comprises multi-axially electrospinning the fluid stock with a
gas or a second fluid stock. In some embodiments, the fluid stock
comprises a non-aqueous solvent. In some embodiments, the fluid
stock comprises tetrahydrofuran (THF) and polystyrene (PS).
[0026] In one aspect, described herein is a process of producing a
nanofiber, the process comprising electrospinning a fluid stock
into an electrospun material, the fluid stock comprising polymer
and precursor, the precursor comprising (i) metal precursor, (ii)
ceramic precursor, or (iii) a combination thereof, and: (a) the
weight to weight ratio of the precursor to polymer being at least
1:2; (b) the fluid stock is (1) a solution; (2) a substantially
uniform dispersion; or (3) a substantially homogenous dispersion;
(c) the concentration of the precursor in the fluid stock is at
least 200 mM; or (d) a combination thereof.
[0027] In some embodiments, the fluid stock is an aqueous fluid
stock.
[0028] In some embodiments, the process further comprises removing
the polymer from the electrospun material.
[0029] In some embodiments, the process further comprises
calcination of the precursor to metal, metal oxide, metal alloy,
ceramic, or a combination thereof.
[0030] In some embodiments, calcination of the metal and/or ceramic
precursor(s) is performed under inert, oxidative, or reductive
conditions.
[0031] In some embodiments, the metal is selected from the group
consisting of Ag, Cu, Ni, Fe, Co, Pb, Au, Sn, and Al.
[0032] In some embodiments, the ceramic or metal oxide is selected
from the group consisting of Al.sub.2O.sub.3, ZrO.sub.2,
Fe.sub.2O.sub.3, CuO, NiO, ZnO, CdO, C, Ge, Si, SiO.sub.2,
TiO.sub.2, V.sub.2O.sub.5, VO.sub.2, Fe.sub.3O.sub.4, SnO,
SnO.sub.2, CoO, CoO.sub.2, Co.sub.3O.sub.4, HfO.sub.2, BaTiO.sub.3,
SrTiO.sub.3, and BaSrTiO.sub.3.
[0033] In some embodiments, the fluid stock comprises the precursor
associated with the polymer by covalent or non-covalent
interactions.
[0034] In some embodiments, the association of the precursor with
the polymer provides a fluid stock comprising precursor uniformly
dispersed therein.
[0035] In some embodiments, the polymer and precursor taken
together comprise about 1 weight % to about 20 weight % of the
fluid stock.
[0036] In some embodiments, the metal precursor comprises a
metal-ligand complex.
[0037] In some embodiments, the metal-ligand complex is a metal
acetate, metal nitrate, metal chloride, or metal alko-oxide.
[0038] In some embodiments, the polymer is a thermally degradable
or chemically degradable polymer.
[0039] In some embodiments, the polymer is polyvinyl alcohol,
polyvinyl acetate, polyvinyl ether, polyvinyl pyrrolidone,
polyglycolic acid, polyethylene oxide, hydroxyethylcellulose (HEC),
ethylcellulose, cellulose ethers, polyacrylic acid, polyisocyanate,
or any combination thereof.
[0040] In some embodiments, the process of electrospinning the
fluid stock comprises electrospinning the fluid stock with a second
fluid stock about the same or similar axis to produce a layered
nanofiber.
[0041] In one aspect, described herein is a nanofiber comprising a
metal, a metal oxide, a metal alloy, a ceramic, a metal precursor,
a ceramic precursor or a combination thereof, and: (a) the
nanofiber is at least 1 .mu.m (e.g., at least 50 .mu.m) long on
average; (b) the nanofiber has an aspect ratio of at least about 5
(e.g., at least 10, at least 100, at least 1000, or the like); (c)
the nanofiber comprises a segment comprising a continuous matrix of
a metal, a metal oxide, a metal alloy, a ceramic, or a combination
thereof; (d) the nanofiber has a specific surface area between 1
m.sup.2/g and about 1000 m.sup.2/g; or (e) a combination thereof.
In some embodiments, the nanofiber comprises at least 33% (w/w) of
a metal, a metal oxide, a metal alloy, a ceramic, a metal
precursor, a ceramic precursor or a combination thereof.
[0042] In some embodiments, the metal is selected from the group
consisting of Ag, Cu, Ni, Fe, Co, Pb, Au, Sn, and Al.
[0043] In some embodiments, the ceramic or metal oxide is selected
from the group consisting of Al.sub.2O.sub.3, ZrO.sub.2,
Fe.sub.2O.sub.3, CuO, NiO, ZnO, CdO, C, Ge, Si, SiO.sub.2,
TiO.sub.2, V.sub.2O.sub.5, VO.sub.2, Fe.sub.3O.sub.4, SnO,
SnO.sub.2, CoO, CoO.sub.2, Co.sub.3O.sub.4, HfO.sub.2, BaTiO.sub.3,
SrTiO.sub.3, and BaSrTiO.sub.3.
[0044] In some embodiments, the nanofiber comprises a conductive
material, wherein the nanofiber has an conductivity of at least
about 10% when compared with the conductivity of the conductive
material when formed into a sheet.
[0045] In one aspect, described herein is a process for producing a
nanofiber, the process comprising electrospinning about the same or
similar axis a first fluid stock with a second fluid stock, the
first fluid stock being aqueous and comprising a first polymer.
[0046] In some embodiments, the first polymer is water soluble.
[0047] In some embodiments, the second fluid is aqueous.
[0048] In some embodiments, the second fluid stock comprises a
second polymer, and the first and second polymers are optionally
the same.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] The novel features of the invention are set forth with
particularity in the appended claims. A better understanding of the
features and advantages of the present invention will be obtained
by reference to the following detailed description that sets forth
illustrative embodiments, in which the principles of the invention
are utilized, and the accompanying drawings of which:
[0050] FIG. 1 illustrates a schematic of the process and system of
the disclosure.
[0051] FIG. 2A illustrates an exemplary mechanism of
precursor-polymer bonding. FIG. 2B illustrates an FTIR study of the
effect of Ni precursor loading on the saturation of --OH bonds in
PVA.
[0052] FIG. 3 illustrates micrographs and an x-ray diffraction plot
of Ni nanofibers from electrospinning of Ni--Ac/PVA (2:1) feed.
[0053] FIG. 4 illustrates micrographs and an x-ray diffraction plot
of NiO nanofibers from electrospinning of Ni--Ac/PVA (2:1)
feed.
[0054] FIG. 5 illustrates micrographs and an x-ray diffraction plot
of Cu nanofibers from electrospinning of Cu--Ac/PVA (2:1)
solution.
[0055] FIG. 6 illustrates micrographs and an x-ray diffraction plot
of CuO nanofibers from electrospinning of Cu--Ac/PVA (2:1)
solution.
[0056] FIG. 7 illustrates micrographs and an x-ray diffraction plot
of Ag nanofibers from electrospinning of Ag--Ac/PVA (2:1)
solution.
[0057] FIG. 8 illustrates micrographs and an x-ray diffraction plot
of Fe nanofibers from electrospinning of Fe--Ac/PVA (2:1)
solution.
[0058] FIG. 9 illustrates micrographs and an x-ray diffraction plot
of ZnO nanofibers from electrospinning of Zn--Ac/PVA (2:1)
solution.
[0059] FIG. 10 illustrates micrographs and an x-ray diffraction
plot of CdO nanofibers from electrospinning of Cd--Ac/PVA (2:1)
solution.
[0060] FIG. 11 illustrates micrographs and an x-ray diffraction
plot of ZrO.sub.2 nanofibers from electrospinning of Zr--Ac/PVA
(2:1) solution.
[0061] FIG. 12 illustrates micrographs and an x-ray diffraction
plot of Pb nanofibers from electrospinning of Pb--Ac/PVA (2:1)
solution.
[0062] FIG. 13 illustrates micrographs demonstrating the effect of
precursor loading on fiber morphology (Ni--Ac/PVA=1:2, 1:1, 2:1 and
4:1).
[0063] FIG. 14 illustrates TEM micrographs demonstrating the
substantial lack of voids in nanofibers (Ni--Ac/PVA=1:2, 1:1, 2:1
and 4:1).
[0064] FIG. 15 illustrates elemental analysis of pure Ni
nanofibers.
[0065] FIG. 16 illustrates micrographs and an x-ray diffraction
plot of ZnO/ZrO.sub.2 hybrid nanofibers.
[0066] FIG. 17 illustrates micrographs and an x-ray diffraction
plot of Ag/ZrO.sub.2 hybrid nanofibers.
[0067] FIG. 18 illustrates micrographs and an x-ray diffraction
plot of Ni/ZrO.sub.2 hybrid nanofibers.
[0068] FIG. 19 illustrates micrographs and an x-ray diffraction
plot of Fe/ZrO.sub.2 hybrid nanofibers.
[0069] FIG. 20 illustrates TEM micrographs of ZrO.sub.2 hybrid
(nanocomposite) nanofibers containing various metal and metal
oxides (ZnO, Ni, Ag, and Fe).
[0070] FIG. 21 illustrates micrographs and an x-ray diffraction
plot of Ni/Al.sub.2O.sub.3 hybrid nanofibers.
[0071] FIG. 22 illustrates micrographs and an x-ray diffraction
plot of CdSe alloy nanofibers.
[0072] FIG. 23 illustrates micrographs and an x-ray diffraction
plot of PbSe alloy nanofibers.
[0073] FIG. 24 illustrates TEM micrographs of CdSe and PbSe alloy
nanofibers.
[0074] FIG. 25 illustrates elemental analysis of PbSe alloy
nanofibers.
[0075] FIG. 26 illustrates micrographs and an x-ray diffraction
plot of CdTe alloy nanofibers.
[0076] FIG. 27 illustrates micrographs and an x-ray diffraction
plot of PbTe alloy nanofibers.
[0077] FIG. 28 illustrates micrographs and an x-ray diffraction
plot of Fe.sub.3O.sub.4/FeNi alloy nanofibers.
[0078] FIG. 29 illustrates TEM micrographs of Fe.sub.3O.sub.4/FeNi
alloy nanofibers.
[0079] FIG. 30 illustrates a graphic comparing the electrical
conductivity of metal nanofibers from various thermal treatment
conditions to the conductivity of a metallic film.
[0080] FIG. 31 illustrates micrographs and an x-ray diffraction
plot of Ni/ZrO.sub.2 hybrid nanofibers.
[0081] FIG. 32 illustrates TEM micrographs of Ni/ZrO.sub.2 hybrid
nanofibers.
[0082] FIG. 33 illustrates elemental analysis of Ni/ZrO.sub.2
hybrid nanofibers.
[0083] FIG. 34 illustrates a schematic of the process and system
for producing Fe/Pt nanofibers suitable for use in fuel cells.
[0084] FIG. 35 illustrates a schematic of the process and system
for producing hollow Si or Ge nanofibers suitable for use in
lithium ion batteries and a micrograph of hollow Si or Ge
electrospun fluid stock.
[0085] FIG. 36 illustrates a schematic of the process and system
for producing Al.sub.2O.sub.3/ITO hybrid nanofibers suitable for
use in flexible solar cells.
[0086] FIG. 37 illustrates micrographs, x-ray diffraction plots and
a schematic for a solar cell with a plurality of components made
from inorganic nanofibers.
[0087] FIG. 38 illustrates a graphic comparing the effect of
calcination conditions on electrical conductivity and magnetic
coercivity of Ni nanofibers.
[0088] FIG. 39 illustrates a graphic comparing the effect of fiber
alignment conditions on electrical conductivity in the axial and
perpendicular direction of a Ni nanofiber mat.
[0089] FIG. 40 illustrates a Ragone plot depicting energy densities
and power densities typical of electrochemical devices.
[0090] FIG. 41 illustrates an exemplary principle of operation and
energy level scheme of a dye-sensitize nanocrystalline solar
cell.
[0091] FIG. 42 illustrates an exemplary principle of operation of a
thin film nanocrystal/nanowire hybrid solar cell.
[0092] FIG. 43 illustrates a schematic of tri-axial
electrospinning.
[0093] FIG. 44 illustrates a TEM image of tri-axial nanofibers of
SiO.sub.2 (core)/PI-b-PS with Fe.sub.3O.sub.4 (middle)/SiO.sub.2
(sheath).
[0094] FIG. 45 illustrates a cross-sectional view of an
electrolytic double layer ultracapacitor.
[0095] FIG. 46 illustrates a cross-sectional view of barium
titanate nanofibers laid on the activated carbon of an
ultracapacitor.
DETAILED DESCRIPTION OF THE INVENTION
[0096] Nanotechnology is the manipulation of matter at an atomic
and molecular scale and is a diverse field involving many different
structures, techniques and potential applications. Of them, one
structure is a nanofiber, which generally has a diameter of less
than 5,000 nm and has various lengths. There is a need for high
quality nanofibers, such as metal nanofibers, ceramic nanofibers,
hybrid nanofibers, and the like. Such nanofibers and processes for
preparing such nanofibers are provided in certain embodiments
herein. In some embodiments, provided herein are high quality
nanofibers that have good structural integrity, few voids, few
structural defects, tunable length, and the like. In some
embodiments, the present disclosure includes methods for making
long, high quality nanofibers.
[0097] In some embodiments, methods provided herein use a fluid
stock comprising a precursor and a polymer that interact with each
other and/or are compatible with each other such that the polymer
facilitates solubilization (e.g., dissolution, dispersion, or the
like) of the precursor. In one aspect, provided herein is a
nanofiber (e.g., a precursor nanofiber) comprising a polymer and a
precursor. In another aspect, provided herein is a nanofiber
comprising a metal component (e.g., a metal, such as a single metal
or a metal alloy, a metal oxide, such as a metal oxide, a ceramic,
or the like). In a specific aspect, provided herein is a continuous
matrix metal component nanofiber. In a more specific aspect,
provided herein is a nanofiber comprising a segment comprising a
continuous matrix of a metal, a metal oxide, a metal alloy, a
ceramic, or a combination thereof.
[0098] In some embodiments, provided herein is a process for the
conversion of electrospun fluid stock (e.g., a precursor nanofiber
comprising a polymer and a precursor) to a nanofiber, wherein the
polymer is removed. In some instances, this process, leaves defects
such as gaps, voids, and the like in the resultant nanofiber. In
some embodiments, these defects are reduced by increasing the
proportion of a metal or ceramic precursor in the fluid stock
relative to the amount of polymer.
[0099] In some embodiments, ensuring that the fluid stock is
homogenous reduces the voids and/or defects in the nanofiber
compared to when the fluid stock is not homogenous. In some
instances, when the fluid feed is electrospun and converted to a
nanofiber, use of homogenous fluid feed leads to a homogenous
nanofiber. In some embodiments, provided herein are methods for
creating homogenous fluid stocks. In some embodiments, the
precursor is solubilized by associating the precursor with a
ligand. In some embodiments, the polymer is water soluble. In some
instances, water-based (aqueous) fluid stocks are advantageous over
fluid stocks based on other solvents (e.g., where a non-aqueous
solvent is toxic). In some embodiments, it is advantageous to
perform the process in an aqueous environment.
[0100] In some embodiments, associating the precursor with the
polymer, such as through a chemical bond between the precursor and
polymer results in long, high quality nanofibers with few defects
compared to embodiments without an association between the
precursor and polymer. In some instances, the precursor is
distributed relatively homogenously on the polymer (e.g., such that
electrospinning of the fluid stock having such homogenous
associations provides nanofibers with few voids and defects). In
addition to the association, it is advantageous in some embodiments
to first create a homogenous solution of precursor before combining
the precursor and polymer.
[0101] In some embodiments, the increased proportion of precursor
and homogenous distribution of the precursor to create high quality
nanofibers results in nanofibers with complex geometries or
advanced properties. These geometries include long hollow
nanofibers and nanofibers that are hybrids of more than one
material. In various embodiments, these materials are without
limitation, metals, ceramics, or combinations thereof.
Process
[0102] Described herein is a process of producing a nanofiber. In
some embodiments, the process includes electrospinning a fluid
stock. In specific embodiments, the fluid stock comprises metal
precursor (e.g., a precursor comprising a metal-ligand compound
that, depending on downstream treatment can be converted into a
metal, a metal oxide, a ceramic, or the like) and polymer. In
specific embodiments, the metal precursor and polymer are present
in a precursor-polymer association. In certain embodiments, the
weight to weight ratio of the precursor to polymer is at least 1:2.
In specific embodiments, the weight to weight ratio of the
precursor to polymer is over 1:2. In more specific embodiments, the
wt. precursor to wt. polymer ratio is at least 1:1. In still more
specific embodiments, the wt. precursor to wt. polymer ratio is
over 1:1. In some embodiments, the polymer is water soluble (e.g.,
completely dissolvable in water, or at least swellable in water).
In specific embodiments, the fluid stock is aqueous (i.e.,
comprising water). In certain embodiments, the precursor (e.g., as
measured by the metal component of the precursor) is at least 200
mM in the fluid stock.
[0103] In some embodiments, provided herein is a process of
electrospinning a fluid stock, the fluid stock comprises metal
precursor and polymer, the weight-to-weight ratio of the precursor
to polymer of over 1:2 (e.g., at least 1:1.75). In certain
embodiments, the fluid stock is prepared by combining precursor and
polymer in a weight-to-weight ratio of over 1:2 (e.g., at least
1:1.75). In specific embodiments, the fluid stock is aqueous. In
more specific embodiments, the metal precursor and polymer are
present in the fluid stock in a precursor-polymer association.
[0104] In some embodiments, a process described herein comprises
associating or binding a metal to a solubilizing ligand to produce
a first metal precursor, optionally in an aqueous solution. In some
embodiments, the precursor solution is mixed to provide a
homogenous precursor composition (e.g., solution). In some
embodiments, the precursor composition is then combined with a
composition of polymer (e.g., water-soluble polymer) to provide a
fluid stock.
[0105] In some embodiments, the (first) precursor molecules
associate with, or bind to (which terms are understood to be used
interchangeably herein--reference to association or binding
indicates formation of a covalent bond, a metal-ligand complex, an
ionic bond, a Lewis base/Lewis acid interaction, or the like), the
polymer (e.g., to provide a precursor-polymer association--a
polymer+a second metal precursor).
[0106] In some embodiments, the fluid stock is mixed to provide a
homogenous fluid stock, where the precursor is optionally
associated with the polymer substantially evenly (e.g., as
determined by measuring the variation of viscosity in the
composition). In some embodiments, the fluid stock is then
electrospun into an electrospun fluid stock. In some instances, the
electrospun fluid stock is then calcinated, optionally by heating.
In some embodiments, heating in a reducing environment results in a
pure metal nanofiber and heating in an oxidizing environment leads
to a ceramic nanofiber.
[0107] In certain embodiments, the polymer is a nucleophilic
polymer (e.g., a polymer comprising alcohol groups, such as PVA).
In some embodiments, the polymer is a nucleophilic polymer and a
first precursor (e.g., reagent precursor) is an electrophilic
precursor (e.g., a metal acetate, metal chloride, or the like). In
specific embodiments, the precursor-polymer association is a
reaction product between a nucleophilic polymer and an
electrophilic first precursor (e.g., reagent precursor).
[0108] In other embodiments, the polymer is an electrophilic
polymer (e.g., a polymer comprising chloride or bromide groups,
such as polyvinyl chloride). In some embodiments, the polymer is an
electrophilic polymer and a first precursor (e.g., reagent
precursor) is a nucleophilic precursor (e.g., metal-ligand complex
comprising "ligands" with nucleophilic groups, such as alcohols or
amines). In specific embodiments, the precursor-polymer association
is a reaction product between an electrophilic polymer and a
nucleophilic first precursor.
[0109] In some embodiments, the fluid stock comprises a high
loading of precursor. In specific embodiments, the fluid stock
comprises a high loading of the precursor on the polymer and/or
associations between the precursor and polymer. In specific
embodiments, the polymer has a precursor loading of at least 20%
(i.e., at least 20% of the reactive sites of the
polymer--nucleophilic or electrophilic sites--are associated with a
metal compound; this is also described herein as being at least 20%
saturated with precursor). As discussed herein, when taken
together, the polymer loaded with metal precursor form (i) a
composition comprising a polymer and a metal precursor and (ii) a
polymer-precursor association. In more specific embodiments, the
polymer has a loading of at least 35%. In still more specific
embodiments, the polymer has a loading of at least 50%. In yet more
specific embodiments, the polymer has a loading of at least 75%.
Loading can be determined by any suitable mechanism, e.g., nuclear
magnetic resonance (NMR) spectrometry, infrared (IR) spectrometry,
or the like. For example, FIG. 2B illustrates the increased loading
of precursor on the polymer (e.g., by the decreasing intensity of
the --OH peak).
[0110] In some instances, the methods for creating a homogenous
fluid stock are used to produce structures with geometries other
than nanofibers (e.g., nanoparticles, spheres, meshes, thin films,
nano-robotic parts such as a gear). As with nanofibers, it is
desirable in some embodiments to make these structures with few
defects, so are suitable applications of the present disclosure. In
one aspect, the present invention includes pure metal, ceramic, or
hybrid nanostructures including spheres, meshes, gears and the
like.
[0111] In some embodiments, the process comprises electrospinning a
fluid stock. Any suitable method for electrospinning is used. In
some instances, elevated temperature electrospinning is utilized.
Exemplary methods for comprise methods for electrospinning at
elevated temperatures as disclosed in U.S. Pat. No. 7,326,043 and
U.S. Pat. No. 7,901,610, which are incorporated herein for such
disclosure. In some embodiments, elevated temperature
electrospinning improves the homogeneity of the fluid stock
throughout the electrospinning process. In some embodiments, gas
assisted electrospinning is utilized (e.g., about a common axis
with the jet electrospun from a fluid stock described herein).
Exemplary methods of gas-assisted electrospinning are described in
PCT Patent Application PCT/US2011/024894 ("Electrospinning
apparatus and nanofibers produced therefrom"), which is
incorporated herein for such disclosure. In gas-assisted
embodiments, the gas is optionally air or any other suitable gas
(such as an inert gas, oxidizing gas, or reducing gas). In some
embodiments, gas assistance increases the throughput of the process
and/or reduces the diameter of the nanofibers. In some instances,
gas assisted electrospinning accelerates and elongates the jet of
fluid stock emanating from the electrospinner. In some embodiments,
incorporating a gas stream inside a fluid stock produces hollow
nanofibers. In some embodiments, the fluid stock is electrospun
using any method known to those skilled in the art.
[0112] In some embodiments, nanofibers are produced from an aqueous
fluid stock (e.g., comprising water, a water soluble polymer and
metal and/or ceramic precursor). In some instances, aqueous fluid
stocks are cheaper, more environmentally friendly, avoid the use of
organic solvents and/or have other advantages in certain
applications. In addition, in certain aspects, the use of aqueous
fluid stocks allows for higher loading of both polymers and
precursors. In some instances, higher precursor loading provides
for metal, metal oxide, and ceramic nanofibers that have good
structural integrity, reduced void structures, and/or reduced
structural defects.
[0113] In specific embodiments, the use of aqueous fluid stocks is
combined with coaxial electrospinning (electrospinning two or more
fluids about a common axis). As described herein, coaxial
electrospinning with a second fluid is used to add coatings, make
hollow nanofibers, make nanofibers comprising more than one
material, and the like. In various embodiments, the second fluid is
either outside (i.e., at least partially surrounding) or inside
(e.g., at least partially surrounded by) the aqueous (first) fluid
stock. In some embodiments, the second fluid is a gas (gas-assisted
electrospinning). As described herein, in some embodiments, gas
assistance increases the throughput of the process, reduces the
diameter of the nanofibers, and/or is used to produce hollow
nanofibers. In some embodiments, the method for producing
nanofibers comprises coaxially electrospinning an aqueous fluid
stock and a gas. In other embodiments, the second fluid is a second
fluid stock having the characteristics as described herein (i.e.,
comprising a polymer and precursor according to the instant
disclosure). In some embodiments where at least two fluid stocks
according to the instant disclosure are coaxial electrospun
according to a method described herein, a hybrid nanofiber
comprising a core and at least one layer thereon is formed.
[0114] In one aspect, described herein is a method for producing a
nanofiber, the method comprising electrospinning a first fluid with
a second fluid, at least one of the first or second fluids being an
aqueous fluid. In various embodiments, the first fluid and second
fluid are positioned relative to each other in any suitable
orientation and/or shape. In some embodiments, the first fluid and
second fluids are next two each other as they exit the
electrospinner. In some embodiments, one of either the first fluid
or second fluid surrounds the other. In some embodiments, the first
and second fluids are electrospun about the same or similar
axis.
[0115] In some embodiments, the first fluid is an aqueous fluid
comprising water, a water soluble polymer, and metal and/or ceramic
precursor. In some embodiments, the second fluid is a second
aqueous fluid, comprising water, a water soluble polymer, and a
second metal and/or ceramic precursor, wherein the water soluble
polymer of the second fluid is the same or different than the water
soluble polymer of the first fluid.
[0116] In some embodiments, the method includes "co-axially"
electrospinning, producing "co-axial" hybrid nanofibers, and such.
As used herein, co-axial refers to concentric cylinders of material
that have a common (the same) center axis (e.g., a cylindrical
nanofiber with a core material surrounded by one or more coatings
or cylindrical layers). Co-axial nanofibers are hollow in some
embodiments. There is no limit to the number of layers of material
(i.e., co-axial does not imply two layers). The terms "co-axial"
and "multi-axial" are used interchangeably. Multi-axial
electrospinning refers to electrospinning multiple fluids (e.g.,
multiple fluid stocks as described herein and/or one or more gas)
about a common axis.
[0117] In some instances, the use of metal precursors increases the
electrical conductivity, which may lead to more vigorous whipping
of the electrospinning filament. Increasing the electrical
conductivity of the fluid stock through choice of precursor for
example, may also increase the productivity of the process in some
instances. In some instances, increased productivity is achieved by
increasing the conductivity of the fluid stock. In certain
instances, increased conductivity causes more repulsion by the jets
emanating from adjacent spinnerets. In some instances, the jets are
less likely to touch each other prematurely because of this
increased repulsion, which allows the practitioner to space the
spinnerets more closely together. More closely spaced spinnerets
generally results into increased overall productivity (as long as
the productivity per spinneret is not substantially reduced).
[0118] The electrospinning process described herein comprises
dispersing and/or keeping the fluid stock relatively evenly
dispersed (e.g., uniformly dispersed or homogenously dispersed). In
some embodiments, to achieve or maintain dispersion, the fluid
stock is heated, especially if the fluid stock solidifies at
ambient temperature. In some embodiments, the fluid stock is
agitated, optionally in combination with heating. Agitation
includes but is not limited to stirring, mixing, sonicating,
vortexing, and the like and creates or maintains a substantially
homogenous fluid stock. In some instances, the fluid stock is
stirred continuously during the electrospinning process. In one
particular embodiment, the fluid stock is stirred for about an hour
to get a homogenous dispersion.
[0119] In some embodiments, the procedure for forming the nanofiber
is not electrospinning Electrospinning is but one method of
producing nanofibers. Other suitable methods include the sol-gel
technique or interfacial polymerization or "fast mixing" techniques
(Huang, Pure Appl. Chem., Vol. 78, No. 1, pp. 15-27, 2006). The
present disclosure further includes methods for making
nano-geometries other than fibers such as for making nano-spheres
by electrospraying. The composition of the fluid stock and methods
for making same are agnostic to the particular geometry (i.e., are
applicable to any geometry) and method for producing the
geometry.
[0120] In some examples, high loading of precursor on the polymer
in the fluid stock is beneficial for obtaining pure and/or uniform
nanofibers. As described herein, few defects and/or voids are
created in the nanofiber when the polymer is removed compared to
the number of defects and/or voids created when having lower
precursor loading. Loading is represented as the weight ratio of
the precursor to polymer in or combined to form the fluid stock.
The weight ratio of the precursor to polymer is any value resulting
in a nanofiber with suitable properties in a given embodiment. The
weight ratio of the precursor to polymer is at least 1:2 in some
embodiments. In some embodiments, there is more precursor than
polymer by weight. In some embodiments, the weight ratio of the
precursor to polymer is at least 1.25:1, at least 1.5:1, at least
1.75:1, at least 2:1, at least 3:1, at least 4:1, at least 5:1, at
least 6:1, at least 7:1, at least 8:1, at least 9:1, at least 10:1,
at least 15:1, at least 20:1, at least 30:1, at least 40:1, at
least 50:1, or at least 100:1. In some embodiments, the weight
ratio of the precursor to polymer is about 1.25:1, about 1.5:1,
about 1.75:1, about 2:1, about 3:1, about 4:1, about 5:1, about
6:1, about 7:1, about 8:1, about 9:1 about 10:1, about 15:1, about
20:1, about 30:1, about 40:1, about 50:1, or about 100:1. In yet
other embodiments, the weight ratio of precursor to polymer is
between about 1:2 and 10:1, between 1:1 and 4:1, between about 2:1
and 10:1, or between about 3:1 and 8:1. In specific embodiments, if
the polymer and precursor present in the fluid stock are present in
the form of a polymer-precursor association, the weight ratio is
determined by comparing the un-associated, un-reacted theoretical
weights of the polymer and the precursor (e.g., a first precursor
that is reacted with the polymer, such as a metal acetate). In some
embodiments, a process described herein comprises preparing and/or
using a fluid stock that is prepared by combining precursor with a
polymer and, optionally, a fluid (e.g., water, or water containing
fluid--an aqueous fluid) and the precursor/polymer weight-to-weight
ratio is determined by the amount of precursor (e.g., a first
precursor) combined with a polymer (e.g., a polymer not associated
with a precursor). For example, if the fluid stock is prepared with
x grams of a precursor (e.g., a first precursor) and y grams of
polymer, the precursor/polymer weight-to-weight ratio is x:y (e.g.,
regardless of whether or not the precursor ultimately associates
with the polymer in the stock). In some embodiments, upon
combination of a precursor (e.g., a first precursor, such as
ML.sub.b, wherein M is a metal and L is one or more ligand as
described herein, and b is a suitable number, such as 1-10) with a
polymer (P), a polymer-precursor association is formed (e.g.,
P-ML.sub.b-1, ML.sub.b-1 being a second precursor in association
with the polymer). In some of such instances, all or part of the
first precursor is associated with the polymer and the
precursor/polymer weight-to-weight ratio is determined by the ratio
of the sum of the first and second precursors to the polymer.
[0121] In some embodiments, a process provided herein comprises:
(a) preparing a fluid stock by combining a first metal precursor, a
polymer, and a fluid (e.g., aqueous fluid), the first fluid
precursor being combined with the polymer in a weight-to-weight
ratio of at least 1:2; and (b) electrospinning a fluid stock. In
other embodiments, a process provided herein comprises
electrospinning a fluid stock prepared by combining a first metal
precursor, a polymer, and a fluid (e.g., aqueous fluid), the first
metal precursor being combined with the polymer in a
weight-to-weight ratio of at least 1:2. In specific embodiments,
upon combination of the metal precursor and the polymer, at least a
portion of the first metal precursor associates with the polymer to
form a polymer-precursor association, the polymer-precursor
association comprising a polymer and a second metal precursor
(i.e., a residual component of the first metal precursor). For
example, FIG. 2A illustrates a first precursor of
Al(OCOCH.sub.3).sub.3 reacting with a polymer to form a
polymer-precursor association comprising a polymer (polyvinyl
alcohol) in association with a second precursor of
Al(OCOCH.sub.3).sub.2. In specific embodiments, the weight to
weight ratio of the first precursor to polymer is over 1:2. In more
specific embodiments, the wt. first precursor to wt. polymer ratio
is at least 1:1. In still more specific embodiments, the wt. first
precursor to wt. polymer ratio is over 1:1.
[0122] In some embodiments, the fluid stock includes metal and/or
ceramic precursor and polymer. In some embodiments, the nanofiber
comprises metal or ceramic precursor and polymer. In some
embodiments, the precursor and/or nanofiber is not metal and/or
ceramic. The methods described herein are used to make
nanostructures that have few voids or defects in some instances
(e.g., no matter the material). The methods for making a
substantially uniform fluid feed described herein (e.g., by
associating precursor substantially uniformly on a polymer) are
applicable to materials other than metals and/or ceramics.
[0123] FIG. 1 illustrates an exemplary schematic of a process
described herein. In some instances, a first composition comprising
metal precursor 101 (e.g., an acetate of Ag, Al, Co, Fe, Ni, Zn,
Zr, Si, etc.) is combined 102 with a second composition comprising
a polymer 103 (e.g., PVA, PVAc, PVEO, etc.) to prepare a fluid
stock comprising a fluid stock composition 104. In some instances,
a fluid stock provided herein is electrospun using, e.g., a syringe
system 105, through a nozzle 106, wherein the nozzle is optionally
heated. In certain embodiments, electrospinning of the fluid stock
produces a precursor nanofiber 108, comprising metal precursor and
polymer (e.g., in a weight ratio of over 1:2 and up to 4:1), the
precursor nanofiber being collected on a collector 107. Treatment
109 (e.g., thermal and/or chemical treatment) of the precursor
nanofiber 108 may then be performed to produce ceramic, metal, or
composite nanofibers (e.g., pure ceramic, metal, or composite
nanofibers) 110.
[0124] FIG. 34 illustrates another exemplary schematic of a process
described herein. In some instances, a first composition comprising
metal precursor 3401 (e.g., an acetate of Ag, Al, Co, Fe, Ni, Zn,
Zr, Si, etc.) is combined 3402 with a second composition comprising
a polymer 3403 (e.g., PVA, PVAc, PEO, etc.) to prepare a fluid
stock comprising a fluid stock composition 3404. In some instances,
a fluid stock is provided 3406 to an apparatus 3408 comprising a
plurality of electrospinning nozzles/needles 3409. In certain
embodiments, the fluid stock is electrospun with another fluid 3407
(e.g., via connection to an air pump) that is also provided to the
apparatus 3409. In some instances, apparatus 3409 comprises a fluid
stock chamber 3410 and a second fluid chamber (e.g., high pressure
gas chamber) 3411. Electrospinning of the fluid stock may then be
electrospun from a center needle or nozzle (e.g., aligned along a
longitudinal axis) 3413 while a second fluid is being coaxially
expressed from an outer needle or nozzle (e.g., aligned along the
same longitudinal axis) 3412. In specific instances, the fluid
stock nozzle (needle) 3413 is optionally heated. In some instances,
e.g., where hollow nanofibers are desired, the gas and fluid stock
chambers and needles may be switched (see, e.g., FIG. 35). In
certain embodiments, electrospinning of the fluid stock produces a
precursor nanofiber 3415, comprising metal precursor and polymer
(e.g., in a weight ratio of over 1:2 and up to 4:1), the precursor
nanofiber being collected on a collector 3414. Treatment 3416
(e.g., thermal and/or chemical treatment) of the precursor
nanofiber 3415 may then be performed to produce ceramic, metal, or
composite nanofibers (e.g., pure ceramic, metal, or composite
nanofibers) 3417. In specific embodiments, the metal nanofiber may
be a metal alloy nanofiber, such as a platinum-iron alloy 3418.
[0125] FIG. 35 illustrates an exemplary schematic of a process for
preparing hollow (i.e., hollow core) metal, metal oxide, or ceramic
nanofibers described herein. In some instances, a fluid stock is
provided to a fluid stock chamber 3502 of an apparatus described
herein. In some instances, the fluid stock chamber comprises a
supply end and a nozzle end, out of which the fluid stock is
electrospun with the assistance of gas, which is provided via a gas
chamber 3501 comprising a supply end and a nozzle end, the nozzle
end being positioned coaxially (i.e., along substantially the same
longitudinal axis) with the nozzle end of the fluid stock chamber
3503. In some embodiments, coaxial electrospinning of the fluid
stock with the gas in such a manner produces a hollow precursor
nanofiber 3506, which may be collected on a collector 3505. The
hollow precursor nanofibers comprising metal precursor and polymer
is illustrated 3506 in FIG. 35. In some instances, these hollow
precursor nanofibers are then treated 3507 (e.g., thermally) to
produce hollow metal nanofibers 3508. Exemplary hollow nanofibers
include hollow Si or Ge nanofibers.
[0126] FIG. 36 illustrates yet another exemplary schematic of a
process described herein, particularly a layered nanocomposite
nanofiber that is prepared by a coaxial gas assisted
electrospinning process. In some instances, a first fluid stock
3601 (e.g., comprising a metal precursor and a polymer), is
electrospun with a second fluid stock 3602 (e.g., comprising a
second metal precursor and a second polymer, the second precursor
and polymer independently being either the same or different from
the first), and a third fluid (e.g., gas) 3603. The fluid stocks
may be provided to the apparatus by any device, e.g., by a syringe
3605. And the gas may be provided from any source 3606 (e.g., air
pump). In some embodiments such an apparatus comprises a plurality
of co-axial needles 3604. Exemplary needles, as illustrates by the
cross section 3707, comprise an outer sheath tube 3608, at least
one intermediate tube 3609, and a core tube 3610. In specific
instances, each of the tubes are coaxially aligned (i.e., aligned
along the substantially same axis). In certain embodiments, such a
process may be utilized to prepare a nanofiber comprising a core
and a layer, wherein the core comprises a metal, metal oxide, or
ceramic, and the layer comprises a metal, metal oxide or ceramic.
In some instances, the core and layer comprise the same or
different materials. In an exemplary embodiment, the core comprises
aluminum (from an aluminum precursor fluid stock), and the layer
may comprise ITO (from an ITO precursor fluid stock).
Precursor Nanofiber
[0127] Provided in certain embodiments, is a nanofiber or a
plurality (used interchangeably herein with "a collection") of
nanofibers comprising a polymer and a metal precursor described
herein. In some embodiments, the nanofiber is prepared according to
a process as described above. In specific embodiments, the polymer
and the metal precursor are present in the nanofiber in the form of
a polymer-precursor association. In some instances, as these
nanofibers are prepared from the fluid stocks described herein,
polymer and precursor ratios of the polymer/precursor nanofibers
are as described herein, e.g., for the fluid stock.
[0128] In some embodiments, the nanofiber(s) comprise polymer and
metal precursor. In some embodiments, the polymer and metal
precursor comprise an optional first metal-precursor and a
polymer-precursor association, the polymer-precursor association
comprising a polymer bound to one or more second metal-precursor.
In some embodiments, the weight ratio of metal precursor to polymer
is at least 1:2 in some embodiments. In other embodiments there is
about equal weights of precursor and polymer. In some embodiments,
there is more precursor than polymer by weight. In some
embodiments, the weight ratio of the precursor to polymer is at
least 1.25:1, at least 1.5:1, at least 1.75:1, at least 2:1, at
least 3:1, at least 4:1, at least 5:1, at least 6:1, at least 7:1,
at least 8:1, at least 9:1, at least 10:1, at least 15:1, at least
20:1, at least 30:1, at least 40:1, at least 50:1, or at least
100:1. In some embodiments, the weight ratio of the precursor to
polymer is about 1.25:1, about 1.5:1, about 1.75:1, about 2:1,
about 3:1, about 4:1, about 5:1, about 6:1, about 7:1, about 8:1,
about 9:1 about 10:1, about 15:1, about 20:1, about 30:1, about
40:1, about 50:1, or about 100:1. In yet other embodiments, the
weight ratio of precursor to polymer is between about 1:2 and 10:1,
between 1:1 and 4:1, between about 2:1 and 10:1, or between about
3:1 and 8:1.
[0129] In some embodiments, a precursor nanofiber provided herein
comprises an optional first metal precursor having the formula
ML.sub.b (wherein M is a metal and L is one or more ligand as
described herein, and b is a suitable number, such as 1-10) and the
polymer-precursor association having the formula
P-(ML.sub.b-1).sub.g (P being a polymer and g being the precursor
saturation or loading number, such a number greater than or equal
to 1). In certain embodiments, g is understood to be a number less
than or equal to the number of monomeric units or reactive sites
(especially if monomeric units having more than one reactive site
are uses) present in P. For example, if approximately 0.0113 moles
(2 g of nickel acetate) reacts completely with 1 g of 79 kDa of
polyvinyl alcohol (approximately 0.0238 moles of vinyl alcohol
monomeric residue), then, without any crosslinking, about 47% of
the alcohols present in the polyvinyl alcohol will have reacted,
and g would be about 884 (0.47 reacted alcohols/polymer*number of
alcohol units/polymer, i.e. 79000 polymer molecular weight/42
alcohol unit molecular weight). In some instances, some
cross-linking between polymers (P), e.g., through a metal
precursor, will be present (e.g., forming a P-ML.sub.b-2-P; if
ML.sub.b, ML.sub.b-1 and ML.sub.b-2 are all present, the ML.sub.b-2
residue may be considered a third metal precursor). In specific
embodiments, combining a first precursor and a polymer under
controlled conditions reduces crosslinking between polymers. In
some embodiments, the polymers are less than 20% cross-linked
(e.g., less than 20% of the metal precursors are associated with 2
or more polymers and/or less than 20% of the monomeric units of the
polymer are connected, e.g., via a metal precursor, to another
polymer). In some embodiments, the polymers are less than 10%
cross-linked. In specific embodiments, the polymers are less than
5% cross-linked. In more specific embodiments, the polymers are
less than 3% cross-linked. In still more specific embodiments, the
polymers are less than 2% cross-linked. In yet more specific
embodiments, the polymers are less than 1% cross-linked.
[0130] In some embodiments, the polymer of the polymer-precursor
association is at least 20% saturated with precursor. In specific
embodiments, the polymer of the polymer-precursor association is at
least 35% saturated with precursor. In more specific embodiments,
the polymer of the polymer-precursor association is at least 50%
saturated with precursor. In still more specific embodiments, the
polymer of the polymer-precursor association is at least 75%
saturated with precursor. In various embodiments, the polymer is
(e.g., on average) at least 20%, at least at least 30%, at least
40%, at least 50%, at least 60%, at least 70%, at least 75%, at
least 80%, at least 85%, at least 85%, at least 90%, at least 95%,
at least 96%, at least 97%, at least 98%, or at least 99%
saturated. In some instances, the polymer is on average between
about 50% and 100%, between about 70% and 100%, between about 90%
and 100%, between about 50% and 90%, between about 60% and 80%, or
between about 20% and 50% saturated.
[0131] In some embodiments, a nanofiber or plurality of nanofibers
provided herein comprise a polymer and (e.g., on average) at least
5 elemental wt. % metal. In certain embodiments, a nanofiber or
plurality of nanofibers provided herein comprise a polymer and
(e.g., on average) at least 10 elemental wt. % metal. In specific
embodiments, a nanofiber or plurality of nanofibers provided herein
comprise a polymer and (e.g., on average) at least 15 elemental wt.
% metal. In more specific embodiments, a nanofiber or plurality of
nanofibers provided herein comprise a polymer and (e.g., on
average) at least 20 elemental wt. % metal. In specific
embodiments, metal constitutes (e.g., on average) at least 25
elemental wt. % of the nanofiber(s). In still more specific
embodiments, metal constitutes (e.g., on average) at least 30
elemental wt. % of the nanofiber(s). In yet more specific
embodiments, metal constitutes (e.g., on average) at least 35
elemental wt. % of the nanofiber(s). In more specific embodiments,
metal constitutes (e.g., on average) at least 40 elemental wt. % of
the nanofiber(s). In various embodiments, metal constitutes (e.g.,
on average) at least 10 elemental wt. %, at least 15 elemental wt.
%, at least 45 elemental wt. %, at least 50 elemental wt. % of the
nanofiber(s).
[0132] In some embodiments, an electrospun precursor nanofiber
comprises metal precursor and polymer, wherein the metal precursor
and polymer when taken together make up at least 50%, at least 60%,
at least 70%, at least 80%, at least 90%, at least 95%, or at least
98% of the total mass of the nanofiber. In specific embodiments,
the polymer is an organic polymer.
[0133] In some instances, the metal precursor of the precursor may
also be optionally solvated (e.g., hydrated if the fluid stock of
the fluid medium is water). It is to be understood that disclosures
herein are intended to contemplate such solvates.
Nanofiber Processing
[0134] In some embodiments, a process provided herein comprises one
or more processes for treating (e.g., further treating for those
embodiments wherein the treatment is combined with the
electrospinning process described above) an electrospun fluid stock
(e.g., a precursor nanofiber comprising a polymer and precursor,
such as any precursor nanofiber described herein). In specific
embodiments, the further treatment comprises converting a precursor
nanofiber (the electrospun nanofiber, comprising a polymer and
precursor) into a metal, metal oxide (e.g., metal oxide ceramic),
or ceramic nanofiber.
[0135] One or all of these treatment processes are collectively
referred to herein as "calcinations". In some embodiments, to
produce a metal, metal oxide, or ceramic nanofiber described herein
(e.g., a pure metal and/or ceramic nanofiber for example), a
process described herein comprises removing the polymer from the
electrospun fluid stock (i.e., precursor nanofiber). In some
embodiments, treatment (calcination) of the precursor nanofiber
includes removing the polymer (e.g., optionally thermally or
chemically removing the polymer). In some embodiments, removing the
polymer creates voids and/or defects in the nanofiber. In some
instances, it is an object of the disclosure to reduce the amount
of polymer in the fluid stock, and/or to employ treatment
(calcination) procedures that lead to reduced voids or defects and
increased nanofiber length and performance. In some instances, the
polymer is removed in a substantially unmodified state. In some
instances, the polymer is degraded by any suitable means (e.g.,
degraded by heat, evaporated, or sublimated). In some instances,
the polymer is removed by chemical means (e.g., by solubilizing the
polymer or chemically degrading the polymer). In some embodiments,
the polymer is chemically degraded in a strong acid or base. In
some embodiments, calcination includes removal of the ligand that
is optionally a component of the precursor. In various embodiments,
the ligand is degraded or removed whole, removed by heat or
chemicals, and the like.
[0136] In some embodiments, the treatment (calcination) process
also comprises converting the precursor(s) to metal (e.g., single
metal, or metal alloy), metal oxide (e.g., metal oxide ceramic),
and/or ceramic. Such a conversion is also intended to be
encompassed herein by the term "calcination". An exemplary
calcination is the conversion of a precursor nanofiber comprising a
polymer and metal and/or ceramic precursors into a metal and/or
ceramic nanofiber. In some embodiments, the conversion of
precursors to metal(s), metal oxide(s), and/or ceramic(s) occurs
simultaneously with the removal of the polymer. In some
embodiments, the conversion of precursors and the removal of the
polymer occur at different times. In various embodiments, polymer
removal and precursor conversion occur under the same conditions,
or under different conditions.
[0137] In some embodiments, treatment (calcination) is performed in
a gaseous environment. In some embodiments (e.g., if one does not
want oxidation reactions to proceed), the gaseous environment is
inert (i.e., consisting of non-reactive gases). In some
embodiments, treatment (calcination) occurs under an inert
atmosphere, such as a noble gas. The noble gases include helium
(He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn),
or mixtures thereof. In specific embodiments, the inert gas is or
comprises argon. In other specific embodiments, the inert gas is or
comprises nitrogen (N.sub.2) gas.
[0138] In some embodiments, treatment of the electrospun fluid
stock comprises chemical treatment thereof. In specific
embodiments, chemical treatment comprises treatment under oxidative
conditions. In some embodiments, oxidative treatment comprises
treating the electrospun fluid stock with a gas comprising oxygen
(e.g., air). In some embodiments, the oxidative treatment also
comprises thermal treatment. In certain chemical reactions occur
upon calcination, optionally oxidation reactions. In some
instances, oxidation converts metal precursors to metal oxide
(e.g., a metal oxide ceramic) or ceramic nanofibers. In some
embodiments, oxidative reactions are performed in an oxygen-rich
environment, such as air. In one particular example (e.g., where
the nanofiber is a ceramic nanofiber), calcination is performed in
air at about 600.degree. C. for about 2 hours.
[0139] In other specific embodiments, chemical treatment comprises
treatment under reduction conditions. Reduction is the gain of
electrons, which is the opposite reaction from oxidation. In some
instances (e.g., such as in the production of pure metal
nanofibers), reducing environments are employed. Here for example,
the reductive environment prevents or minimizes the conversion of
metal precursors to metal oxides (and/or may reduce metal oxides
back to metals if oxidation has occurred). In some embodiments, the
reducing environment comprises metal such as Mg under vacuum. In
some embodiments, the reducing environment comprises hydrogen gas
(H.sub.2). In specific embodiments, the reductive environment is a
mixture of inert gas and hydrogen gas. In some embodiments, the
strength of the reductive environment is varied by blending H.sub.2
with an inert gas in various proportions. The present disclosure
encompasses hydrogen-nitrogen mixtures and the like. In some
embodiments, the reductive environment is any environment in which
oxidation is prevented or minimized (e.g., an environment
substantially devoid of oxygen). In one particular instance,
treatment (calcination) is performed under a mixture of argon and
hydrogen at about 800.degree. C. for about 2 hours to produce a
pure metal nanofiber.
[0140] In some embodiments, treatment (calcination) is performed in
a liquid environment. In some embodiments, the liquid environment
is aqueous. In other embodiments, the liquid environment comprises
a different solvent than water, such as an organic solvent. In some
embodiments, the liquid environments comprise oxidative, reductive,
or inert conditions. An exemplary liquid-based reducing environment
is a solution NaBH.sub.4. An exemplary oxidizing solution comprises
hydrogen peroxide H.sub.2O.sub.2. In some embodiments, calcination
uses a catalyst (i.e., whether conducted in the gas phase or liquid
phase).
[0141] Calcination is performed at any suitable temperature for any
suitable amount of time. In some instances, higher temperature
calcinations produce nanofibers of a smaller diameter. In some
instances, low temperature and/or short time may generate small
crystal domains in amorphous metal or metal oxides, while high
temperature calcination may lead to nanofibers with pure metal or
pure metal oxide crystals. In certain instances, crystal size may
impact electric conductivity or magnetic properties. In some
instances, low temperature calcination of magnetically active metal
or metal oxides may generate superparamagnetic nanofibers. In some
instances, high temperature calcination may produce metal
nanofibers with increased electric conductivity.
[0142] In some embodiments, calcination is performed at about
100.degree. C., about 150.degree. C., about 200.degree. C., about
300.degree. C., about 400.degree. C., about 500.degree. C., about
600.degree. C., about 700.degree. C., about 800.degree. C., about
900.degree. C., about 1,000.degree. C., about 1,500.degree. C.,
about 2,000.degree. C., and the like. In some embodiments,
calcination is performed at a temperature of at least 100.degree.
C., at least 150.degree. C., at least 200.degree. C., at least
300.degree. C., at least 400.degree. C., at least 500.degree. C.,
at least 600.degree. C., at least 700.degree. C., at least
800.degree. C., at least 900.degree. C., at least 1,000.degree. C.,
at least 1,500.degree. C., at least 2,000.degree. C., and the like.
In some embodiments, calcination is performed at a temperature of
at most 100.degree. C., at most 150.degree. C., at most 200.degree.
C., at most 300.degree. C., at most 400.degree. C., at most
500.degree. C., at most 600.degree. C., at most 700.degree. C., at
most 800.degree. C., at most 900.degree. C., at most 1,000.degree.
C., at most 1,500.degree. C., at most 2,000.degree. C., and the
like. In some embodiments, calcination is performed at a
temperature of between about 300.degree. C. and 800.degree. C.,
between about 400.degree. C. and 700.degree. C., between about
500.degree. C. and 900.degree. C., between about 700.degree. C. and
900.degree. C., between about 800.degree. C. and 1,200.degree. C.,
and the like. In specific embodiments, calcination is performed
between 300.degree. C. and 1200.degree. C. In more specific
embodiments, calcination is performed between 400.degree. C. and
1000.degree. C. In still more specific embodiments, calcination is
performed between 500.degree. C. and 900.degree. C. In some
specific embodiments, calcination is performed at 600.degree. C. In
other specific embodiments, calcination is performed at 800.degree.
C.
[0143] In some embodiments, calcination is performed at a constant
temperature. In some embodiments, the temperature changes over
time. In some embodiments, the temperature increases from a first
temperature (e.g., the temperature of the electrospinning process,
optionally room temperature) to a second temperature. In some
embodiments, calcination then proceeds for a given time at the
second temperature. In some embodiments, the temperature continues
to vary. The rate of increase in temperature during calcination is
varied in certain instances. Any suitable rate of increase is
permissible, whereby a nanofiber of the desired properties is
obtained. In certain embodiments, the rate of temperature increase
is about 0.1.degree. C./min. about 0.3.degree. C./min, about
0.5.degree. C./min, about 0.7.degree. C./min, about 1.0.degree.
C./min, about 1.5.degree. C./min, about 2.degree. C./min, about
2.5.degree. C./min, about 3.degree. C./min, about 4.degree. C./min,
about 5.degree. C./min, about 10.degree. C./min, about 20.degree.
C./min, and the like. In certain embodiments, the rate of
temperature increase is at least about 0.1.degree. C./min, at least
about 0.3.degree. C./min, at least about 0.5.degree. C./min, at
least about 0.7.degree. C./min, at least about 1.0.degree. C./min,
at least about 1.5.degree. C./min, at least about 2.degree. C./min,
at least about 2.5.degree. C./min, at least about 3.degree. C./min,
at least about 4.degree. C./min, at least about 5.degree. C./min,
at least about 10.degree. C./min, at least about 20.degree. C./min,
and the like. In some embodiments, the rate of temperature increase
is at most about 0.1.degree. C./min, at most about 0.3.degree.
C./min, at most about 0.5.degree. C./min, at most about 0.7.degree.
C./min, at most about 1.0.degree. C./min, at most about 1.5.degree.
C./min, at most about 2.degree. C./min, at most about 2.5.degree.
C./min, at most about 3.degree. C./min, at most about 4.degree.
C./min, at most about 5.degree. C./min, at most about 10.degree.
C./min, at most about 20.degree. C./min, and the like. In yet other
embodiments, the rate of temperature increase is between about
0.1.degree. C./min and 0.5.degree. C./min, between about
0.5.degree. C./min and 2.degree. C./min, between about 2.degree.
C./min and 10.degree. C./min, between about 0.1.degree. C./min and
2.degree. C./min, and the like.
[0144] Calcination is performed for any suitable amount of time
(e.g., as necessary to arrive at a nanofiber with the desired
properties). In some embodiments, the time and temperature of
calcination are related to each other. For example, choice of a
higher temperature reduces the amount of time needed to produce a
nanofiber with a given property. The converse is also true;
increasing the time of calcination reduces the necessary
temperature, which is advantageous if the nanofiber includes
temperature-sensitive materials for example. In some embodiments,
calcination is performed for about 5 minutes, about 15 minutes,
about 30 minutes, about 1 hour, about 2 hours, about 3 hours, about
4 hours, about 8 hours, about 12 hours, about 1 day, about 2 days,
and the like. In some embodiments, calcination is performed for at
least 5 minutes, at least 15 minutes, at least 30 minutes, at least
1 hour, at least 2 hours, at least 3 hours, at least 4 hours, at
least 8 hours, at least 12 hours, at least 1 day, at least 2 days,
and the like. In some embodiments, calcination is performed for at
most 5 minutes, at most 15 minutes, at most 30 minutes, at most 1
hour, at most 2 hours, at most 3 hours, at most 4 hours, at most 8
hours, at most 12 hours, at most 1 day, at most 2 days, and the
like. In yet other embodiments, calcination is performed for
between about 10 minutes and 60 minutes, between about 1 hour and
about 5 hours, between about 5 hours and 1 day, and the like.
[0145] In some instances, calcination of a precursor nanofiber
results in a desired nanofiber (e.g., a pure metal or pure ceramic
nanofiber). In some embodiments, the nanofiber consists essentially
of pure metal or ceramic (i.e., optionally including small amounts
of other materials). In some embodiments, the other materials are
residual polymer, residual carbonaceous material (e.g., degraded
ligand and/or polymer), minor amounts of oxygen (e.g., in the form
of a metal oxide if the nanofiber is "pure metal"), or other
components of the fluid stock.
[0146] In one aspect, the process has a high yield (e.g., which is
desirable for embodiments in which the precursor is expensive).
Yield may be quantified by comparing the number of molecules (e.g.,
in moles) of precursor molecules in the nanofiber to the number of
molecules (e.g., in moles) of precursor molecules that get
converted into their final form (e.g., metal, metal oxide, or
ceramic) and are incorporated in the nanofiber. In other words, the
yield may be calculated by solving for the number of precursor
molecules (or y*the number of precursor molecules if the precursor
molecule has more than one metal atom (i.e., y metal atoms)
therein) in the fluid stock divided by the number of metal atoms in
the nanofiber(s) (i.e., metal atoms in fluid stock/metal atoms in
nanofiber(s)). In some instances, higher loading of precursor on
the polymer may result in higher yield. For example, in one trial
loading precursor to polymer at a ratio of 4:1 resulted in an 80%
yield. In some embodiments, the metal atoms in the nanofiber are
about 10%, about 20%, about 30%, about 33%, about 40%, about 50%,
about 60%, about 70%, about 80%, about 90%, about 95%, about 98%,
or about 100% of the number of (e.g., in moles) precursor molecules
in the fluid stock. In some embodiments, the metal atoms in the
nanofiber are at least 10%, at least 20%, at least 30%, at least
33%, at least 40%, at least 50%, at least 60%, at least 70%, at
least 80%, at least 90%, at least 95%, at least 98%, or at least
99% of the moles of precursor molecules in the fluid stock. In some
embodiment, the moles of precursor molecules in the nanofiber are
between about 10% and about 40%, between about 20% and about 50%,
or between about 50% and about 100% of the moles of precursor
molecules in the fluid stock.
Fluid Stock
[0147] Described herein are fluid stocks, fluid stocks having
certain characteristics, fluid stocks prepared according to the
methods herein disclosed, fluid stocks preparable by the methods
herein disclosed, fluid stocks incorporating the precursors herein
disclosed, fluid stocks incorporating the polymers herein
disclosed, and fluid stocks suitable for the methods and systems
herein disclosed. The present disclosure also includes methods for
using the fluid stocks, and the like.
[0148] In some embodiments, a composition (e.g., for use as an
electrospinning fluid stock) provided or used in a process herein
comprises metal precursor and polymer. In some embodiments, the
metal precursor is present in a weight-to-weight ratio of over 1:2
with the polymer. In specific embodiments, the metal precursor is
present in a weight-to-weight ratio of over 1:1 with the polymer.
In other embodiments, the precursor to polymer weight ratio is as
described throughout this disclosure. In certain embodiments, the
fluid stock further comprises water (i.e., the fluid stock is
aqueous). In some embodiments, the metal precursor is present in a
concentration of at least 200 mM. In other embodiments, the
precursor is present in any suitable amount described herein. In
various embodiments, the fluid stock comprises a substantially
uniform and/or homogenous dispersion or solution (e.g., as measured
by viscosity deviations, UV absorbance, or the like).
[0149] In specific embodiments, the fluid stock comprises at least
two different metal precursors. In more specific embodiments, the
at least two different metal precursors comprise different metals.
In certain embodiments, use of at least two different metal
precursors provides an alloy or composite nanofiber following
electrospinning and treatment according to the processes described
herein.
[0150] In specific embodiments, metal precursor of the fluid stock
is at least partially in the form of a polymer-precursor
association. In more specific embodiments, the metal precursor is
partially in the form of a polymer-precursor association (e.g.,
P-(ML.sub.b-1).sub.g as described herein) and partially in a form
that is not associated with a polymer (e.g., ML.sub.b as described
herein). In specific embodiments, the precursor present in the
fluid stock is at least 80% associated with the polymer. In more
specific embodiments, the precursor present in the fluid stock is
at least 90% associated with the polymer. In still more specific
embodiments, the precursor present in the fluid stock is at least
95% associated with the polymer. In other specific embodiments, the
precursor present in the fluid stock is at least 20%, at least 30%,
at least 40%, at least 50%, at least 60%, at least 70%, at least
75%, at least 85%, at least 98%, or at least 99% associated with
the polymer. In some instances, some cross-linking between polymers
(P), e.g., through a metal precursor, will be present (e.g.,
forming a P-ML.sub.b-2-P; which is considered to be in "associated"
form). In some embodiments, the polymers of a fluid stock described
herein are less than 20% cross-linked (e.g., less than 20% of the
metal precursors are associated with 2 or more polymers and/or less
than 20% of the monomeric units of the polymer are connected, e.g.,
via a metal precursor, to another polymer). In some embodiments,
the polymers are less than 10% cross-linked. In specific
embodiments, the polymers are less than 5% cross-linked. In more
specific embodiments, the polymers are less than 3% cross-linked.
In still more specific embodiments, the polymers are less than 2%
cross-linked. In yet more specific embodiments, the polymers are
less than 1% cross-linked.
[0151] In some instances, increasing the amount of precursor
relative to the amount of polymer and/or distributing the precursor
relatively uniformly in the fluid stock produces nanofibers with
reduced voids and/or fewer defects relative to nanofibers where the
amount of precursor is lower or the fluid stock is not uniform.
[0152] In some embodiments, the fluid stock is a solution,
optionally an aqueous solution. In some embodiments, the polymer is
water soluble and the precursor is solubilized by associating with
a ligand. In some embodiments, one or more components are not fully
dissolved and the fluid stock is a dispersion. In some instances,
the fluid stock is uniform or homogenous (e.g., no matter whether
the fluid stock is a solution or dispersion). In some embodiments,
homogeneity and/or uniformity of the fluid stock is determined by
measuring the standard deviation of the viscosity of the fluid
stock. In certain embodiments, the viscosity of fractions of the
fluid stock deviate from the viscosity of the fluid stock as a
whole by less than 5%, less than 10%, less than 20%, or any
suitable amount to effectively produce nanofibers described
herein.
[0153] In some embodiments, the fluid stock is kept uniform or
homogenous, e.g., by agitating. In some embodiments, a process
described herein further comprises maintaining uniformity of the
fluid stock, e.g., by heating and/or agitating the fluid stock.
Methods of agitating include, by way of non-limiting example,
mixing, stirring, shaking, sonicating, or otherwise inputting
energy to prevent or delay the formation of more than one phase in
the fluid stock. Any of these methods or equivalents are employed
in various embodiments. In some embodiments, the fluid stock is
continually agitated. In some embodiments, the fluid stock is
agitated to create a uniform dispersion or solution, which is then
used in an electrospinning step before the fluid stock (e.g.,
dispersion or solution) loses uniformity and/or homogeneity (e.g.,
it before it separates into more than one phase). Exemplary phases
are an aqueous phase and an oil phase, or an aqueous phase and a
phase that includes polymer or precursor (e.g., a solid/precipitate
phase) for example.
[0154] In some embodiments, a uniform fluid stock is made by first
agitating a solution of precursor or uniform dispersion of
precursor. In some embodiments, the fluid stock is made by
uniformly distributing precursor in a first dispersion before
combining the first dispersion with a second dispersion (e.g.,
which includes polymer). The precursor solution or uniform
dispersion is continually agitated in some embodiments, optionally
mixed while being combined with the polymer dispersion to create
the fluid stock.
[0155] In some embodiments, the fluid stock is an aqueous fluid
stock and/or comprises polymer dissolved in water. In some
embodiments, the continuous phase of the fluid stock is water
(e.g., when the fluid stock is a dispersion). In some embodiments,
the solvent is water (e.g., when the fluid stock is a solution). In
various embodiments, the solution or dispersion of precursor is
aqueous, the solution or dispersion of polymer is aqueous, or both
solutions or dispersions are aqueous.
[0156] In some embodiments, the fluid stock is heated (e.g.,
optionally in combination with agitation) to create a substantially
uniform or substantially homogenous dispersion or solution. In some
embodiments, the fluid stock is made by uniformly distributing
precursor in a first dispersion before combining the first
dispersion with a second dispersion (e.g., which includes polymer).
In some embodiments, the first dispersion is heated, optionally in
combination with agitation.
[0157] In some embodiments, the polymer concentration in the fluid
stock is related to (e.g., proportional to) the average molecular
weight of the polymer. For example, in some embodiments when the
polymer has a molecular weight of about 1,000,000 atomic mass
units, the polymer is present at 1% of the fluid stock by weight.
In another example, when the polymer has a molecular weight of
about 50,000 atomic mass units, the polymer is present at 20% of
the fluid stock by weight. In general, the higher the molecular
weight of the polymer, the lower the required concentration of
polymer in the fluid stock to achieve high quality metal and/or
ceramic nanofibers.
[0158] The fluid stock contains any suitable amount of polymer. The
weight percent of polymer in the fluid stock is represented as the
weight percent of polymer alone, or as the combined weight percent
of polymer with associated precursor. In some embodiments, the
fluid stock is about 10 weight % polymer or polymer associated with
precursor. In other embodiments, the fluid stock comprises about
0.5 weight %, about 1 weight %, about 2 weight %, about 3 weight %,
about 4 weight %, about 5 weight %, about 6 weight %, about 7
weight %, about 8 weight %, about 9 weight %, about 10 weight %,
about 12 weight %, about 14 weight %, about 16 weight %, about 18
weight %, about 20 weight %, about 30 weight %, or about 40 weight
% polymer or polymer associated with precursor. In some
embodiments, the fluid stock comprises at least about 0.5 weight %,
at least about 1 weight %, at least about 2 weight %, at least
about 3 weight %, at least about 4 weight %, at least about 5
weight %, at least about 6 weight %, at least about 7 weight %, at
least about 8 weight %, at least about 9 weight %, at least about
10 weight %, at least about 12 weight %, at least about 14 weight
%, at least about 16 weight %, at least about 18 weight %, at least
about 20 weight %, at least about 30 weight %, or at least about 40
weight % polymer or polymer associated with precursor. In some
embodiments, the fluid stock comprises at most about 0.5 weight %,
at most about 1 weight %, at most about 2 weight %, at most about 3
weight %, at most about 4 weight %, at most about 5 weight %, at
most about 6 weight %, at most about 7 weight %, at most about 8
weight %, at most about 9 weight %, at most about 10 weight %, at
most about 12 weight %, at most about 14 weight %, at most about 16
weight %, at most about 18 weight %, at most about 20 weight %, at
most about 30 weight %, or at most about 40 weight % polymer or
polymer associated with precursor. In some embodiments, the fluid
stock comprises from about 1 weight % to about 20 weight % polymer
or polymer associated with precursor. In some embodiments, the
fluid stock comprises from about 1 weight % to about 10 weight %,
from about 1 weight % to about 5 weight %, from about 5 weight % to
about 20 weight %, from about 5 weight % to about 10 weight %, from
about 10 weight % to about 15 weight %, or from about 15 weight %
to about 20 weight % polymer or polymer associated with
precursor.
[0159] In certain embodiments, polymer concentration in the fluid
stock is determined on a monomeric residue concentration. In other
words, the concentration of the polymer is determined based on the
concentration of polymeric repeat units present in the stock. For
example, polymer concentration of polyvinyl alcohol may be measured
based on the concentration of (--CH.sub.2CHOH--) present in the
fluid stock. In some embodiments, the monomeric residue (i.e.,
repeat unit) concentration of the polymer in the fluid stock is at
least 100 mM. In specific embodiments, the monomeric residue (i.e.,
repeat unit) concentration of the polymer in the fluid stock is at
least 200 mM. In more specific embodiments, the monomeric residue
(i.e., repeat unit) concentration of the polymer in the fluid stock
is at least 400 mM. In still more specific embodiments, the
monomeric residue (i.e., repeat unit) concentration of the polymer
in the fluid stock is at least 500 mM. In at least 5 mM, at least
100 mM, at least 150 mM, at least 200 mM, at least 250 mM, at least
300 mM, at least 350 mM, at least 400 mM, at least 500 mM, at least
700 mM, at least 900 mM, at least 1.2 M, at least 1.5 M, at least 2
M, at least 5 M, and the like. In some embodiments, the
concentration of the precursor in the fluid stock is between 5 mM
and 5 M, between 200 mM and 1 M, between 100 mM and 700 mM, and the
like. In some embodiments, the concentration of precursor in the
fluid stock to monomeric residue in the fluid stock is at least
1:4. In specific embodiments, the concentration of precursor in the
fluid stock to monomeric residue in the fluid stock is at least
1:3. In more specific embodiments, the concentration of precursor
in the fluid stock to monomeric residue in the fluid stock is at
least 1:2. In still more specific embodiments, the concentration of
precursor in the fluid stock to monomeric residue in the fluid
stock is at least 1:1.2. In yet more specific embodiments, the
concentration of precursor in the fluid stock to monomeric residue
in the fluid stock is about 1:1 (e.g., within 5%). In other
embodiments, the concentration of precursor in the fluid stock to
monomeric residue in the fluid stock is at least 1:10, at least
1:8, at least 1:6, at least 1:1.5, at least 1:3.5, at least 1:2.5,
or any suitable ratio.
[0160] In some embodiments, the fluid stock comprises precursor and
polymer, wherein at least 5 elemental wt. % of the total mass of
the precursor and polymer is metal. In certain embodiments, at
least 10 elemental wt. % of the total mass of the precursor and
polymer is metal. In specific embodiments, at least 15 elemental
wt. % of the total mass of the precursor and polymer is metal. In
more specific embodiments, at least 20 elemental wt. % of the total
mass of the precursor and polymer is metal. In specific
embodiments, at least 25 elemental wt. % of the total mass of the
precursor and polymer is metal. In still more specific embodiments,
at least 30 elemental wt. % of the total mass of the precursor and
polymer is metal. In yet more specific embodiments, at least 35
elemental wt. % of the total mass of the precursor and polymer is
metal. In more specific embodiments, at least 40 elemental wt. % of
the total mass of the precursor and polymer is metal. In various
embodiments, at least 10 elemental wt. %, at least 15 elemental wt.
%, at least 45 elemental wt. %, at least 50 elemental wt. % of the
total mass of the precursor and polymer is metal.
[0161] In one aspect, the concentration of precursor in the fluid
stock is high. The concentration is any suitable concentration. In
some embodiments, the concentration of the precursor in the fluid
stock is about 5 mM, about 10 mM, about 20 mM, about 40 mM, about
60 mM, about 80 mM, about 100 mM, about 150 mM, about 200 mM, about
250 mM, about 300 mM, about 350 mM, about 400 mM, about 500 mM,
about 700 mM, about 900 mM, about 1.2 M, about 1.5 M, about 2 M,
about 5 M, and the like. In some embodiments, the concentration of
the precursor in the fluid stock is at least 5 mM, at least 10 mM,
a at least 20 mM, at least 40 mM, at least 60 mM, at least 80 mM,
at least 100 mM, at least 150 mM, at least 200 mM, at least 250 mM,
at least 300 mM, at least 350 mM, at least 400 mM, at least 500 mM,
at least 700 mM, at least 900 mM, at least 1.2 M, at least 1.5 M,
at least 2 M, at least 5 M, and the like. In some embodiments, the
concentration of the precursor in the fluid stock is at most 5 mM,
at most 10 mM, a at most 20 mM, at most 40 mM, at most 60 mM, at
most 80 mM, at most 100 mM, at most 150 mM, at most 200 mM, at most
250 mM, at most 300 mM, at most 350 mM, at most 400 mM, at most 500
mM, at most 700 mM, at most 900 mM, at most 1.2 M, at most 1.5 M,
at most 2 M, at most 5 M, and the like. In some embodiments, the
concentration of the precursor in the fluid stock is between 5 mM
and 5 mM, between 20 mM and 1 M, between 100 mM and 700 mM, between
100 mM and 300 mM, and the like.
[0162] In some embodiments, a fluid stock is prepared by (i)
dissolving or dispersing a precursor in a first fluid (e.g., water,
or another aqueous medium) to form a first composition; (ii)
dissolving or dispersing a polymer in a second fluid (e.g., water,
or another aqueous medium) to form a second composition; and (iii)
combining at least a portion of the first and second compositions
to form the fluid stock.
Precursor
[0163] In some embodiments, a metal precursor provided herein may
be present in a fluid stock described herein, present in a
precursor nanofiber described herein, used in an electrospinning
process described herein, or the like. In some embodiments, the
precursor is any molecule or molecules convertible into a metal,
ceramic, or metal oxide (such as a metal oxide ceramic). In many
instances, metal precursors are optionally converted, upon
treatment of the precursor (e.g., the precursor present in a
precursor/polymer nanofiber), into a metal (e.g., a single metal, a
metal alloy), a metal oxide (e.g., a metal oxide ceramic) or a
ceramic (e.g., metal oxide, or otherwise). In some embodiments, the
precursor is a molecule or molecules that associates with polymers,
such as those described herein. In some embodiments, the precursor
is a molecule or molecules that distributes substantially uniformly
along the polymers or within the fluid stock. In some embodiments,
an increased weight ratio of precursor in the fluid stock and
distribution of the precursor uniformly in the fluid stock results
in high quality nanofibers with few voids and/and defects (e.g.,
compared with a nanofiber where the weight ratio is lower or the
fluid stock is not uniform).
[0164] Described herein is precursor, precursor having certain
characteristics, precursor prepared according to the methods herein
disclosed, precursor preparable by the methods herein disclosed,
precursor incorporating the ligands herein disclosed, precursor
incorporating the metals herein disclosed, and precursor suitable
for the methods and systems herein disclosed. Also described herein
are methods for using the precursor to produce nanofibers, includes
the nanofibers comprising (precursor nanofibers) and/or prepared by
the precursors (e.g., metal-, metal oxide-, ceramic-containing
nanofibers), and the like.
[0165] In some embodiments, the precursor is a metal containing
compound that is associated with at least one ligand. In certain
embodiments, the metal-ligand association (used interchangeably
herein with "metal-ligand complex") is associated via any suitable
type of bond or interaction. In specific embodiments, the
interaction between the metal and the ligand in the metal-ligand
association (metal-ligand complex) is an ionic bond (e.g., cationic
metal-anionic ligand salt), a covalent bond, a metal-ligand complex
(e.g., coordination complex between ligand and metal), or the like.
In some instances a precursor described herein is associated with a
polymer instead of, or in addition to, other ligands--such
compounds are intended to be considered was metal-ligand
associations (whether or not additional ligands are present).
[0166] In some embodiments, a precursor provided herein is a metal
compound in association with a ligand and free of any association
with a polymer (e.g., ML.sub.b, wherein M is metal and L is one or
more ligand as described herein, and b is a suitable number, such
as a number of at least 1, e.g., 1-10); a metal compound is
association with a polymer and, optionally, in association with a
ligand (e.g., P-ML.sub.b-1, ML.sub.b-1 being a second precursor in
association with the polymer (P); with a ligand if b is >1); a
metal compound in association with more than one polymer and,
optionally, in association with a ligand (e.g., P-ML.sub.b-2-P;
with a ligand if b is >2).
[0167] In some embodiments, the precursor is a molecule that is
substantially identical to the material comprising the nanofiber,
optionally a metal. In some embodiments, the precursor is
convertible to the material comprising the nanofiber. The precursor
is converted by performing the calcination procedures disclosed
herein. For example, in some embodiments, metal precursors in
complex with a ligand are converted to metal oxide nanofibers by
employing oxidizing conditions and heat. In another example,
precursors of metal in complex with a ligand are converted to a
metal nanofiber by calcinating in reducing conditions and heat. In
yet another example, precursors of metal in complex with a ligand
are converted to a metal nanofiber by calcinating in inert
conditions and heat. In other embodiments, these processes may be
performed in the absence of heat.
[0168] In some embodiments, pure metal or ceramic nanofibers have
attractive properties such as high conductivity for use in devices
such as batteries, ultracapacitors, solar cells, and the like. In
some embodiments, nanofibers are also useful in the field of
catalysis on account of the high surface area to volume ratio. In
some embodiments, the precursor comprises a metal. In various
instances, the metal is a transition metal, alkali metal, alkaline
earth metal, post-transition metal, lanthanide, or actinide.
Transition metals include: scandium (Sc), titanium (Ti), vanadium
(V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel
(Ni), copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium
(Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium
(Rh), palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf),
tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium
(Ir), platinum (Pt), gold (Au), mercury (Hg), rutherfordium (Rf),
dubnium (Db), seaborgium (Sg), bohrium (Bh), and hasium (Hs).
Alkali metals include: lithium (Li), sodium (Na), potassium (K),
rubidium (Rb), cesium (Cs) and francium (Fr). Alkaline earth metals
include: beryllium (Be), magnesium (Mg), calcium (Ca), strontium
(Sr), barium (Ba), and radium (Ra). Post-transition metals include:
aluminum (Al), gallium (Ga), indium (In), tin (Sn), thallium (Tl),
lead (Pb), and bismuth (Bi). Lanthanides include the elements with
atomic number 57 to 71 on the periodic table. Actinides include the
elements with atomic number 89 to 103 on the periodic table. In
addition, silicon (Si), germanium (Ge), antimony (Sb) and polonium
(Po) are considered metals for the purposes of the present
disclosure. In some embodiments, silicon is used in the process
described herein to produce silicon nanofibers. In specific
embodiments, the metal of the precursor is a transition metal. In
some specific embodiments, the metal of the precursor is silicon.
In other specific embodiments, the metal of the precursor is not
silicon. In further or alternative embodiments, the metal of the
precursor is aluminum. In other specific embodiments, the metal of
the precursor is not aluminum. In some embodiments, the precursor
comprises at least two different metals.
[0169] In specific embodiments, the metal is an alkali metal. In
other specific embodiments, the metal is an alkaline earth metal.
In still other embodiments, the metal is a transition metal. In
more specific embodiments, the metal is a period IV transition
metal. In other specific embodiments, the metal is a period V
transition metal. In some embodiments, the metal is a group XIII
metal. In certain embodiments, the metal is a group XIV metal. In
certain embodiments, the metal is a metalloid. In specific
embodiments, the metal is lithium, beryllium, sodium, magnesium,
aluminum, silicon, potassium, calcium, titanium, vanadium,
chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium,
germanium, zirconium, palladium, silver, cadmium, tin, barium,
hafnium, tungsten, lead, or the like.
[0170] In specific embodiments, the precursor comprises at least
two precursors (i.e., at least a first and second precursor), each
precursor comprising a different metal than the other precursor. In
specific embodiments, at least one of the metals is silicon. In
other specific embodiments, at least one of the metals is aluminum.
In still other embodiments, at least one of the metals is
zirconium. In some embodiments, the metal of the first precursor is
silicon, aluminum, or zirconium, and the metal of the second
precursor is not silicon, aluminum, or zirconium.
[0171] In specific embodiments, the metal precursor is a
metal-ligand association (complex) (e.g., a coordination complex),
each metal precursor comprising metal atom(s) associated
(complexed) with one or more ligand(s) (e.g., 1-10, 2-9, or any
suitable number of ligands). In specific embodiments, the precursor
described herein comprises at least two different types of ligand
(e.g., at least one acetate and at least one halide). In some
embodiments, the precursor is a metal carboxylate (e.g.,
--OCOCH.sub.3 or another --OCOR group, wherein R is an alkyl,
substituted alkyl, aryl, substituted aryl, or the like). In
specific embodiments, the precursor is lithium acetate, beryllium
acetate, sodium acetate, magnesium acetate, aluminum acetate,
silicon acetate, potassium acetate, calcium acetate, titanium
acetate, vanadium acetate, chromium acetate, manganese acetate,
iron acetate, cobalt acetate nickel acetate, copper acetate, zinc
acetate, gallium acetate, germanium acetate, zirconium acetate,
palladium acetate, silver acetate, cadmium acetate, tin acetate,
barium acetate, hafnium acetate, tungsten acetate, lead acetate, or
the like. In certain embodiments, the precursor is a metal nitrate.
In specific embodiments, the precursor is lithium nitrate,
beryllium nitrate, sodium nitrate, magnesium nitrate, aluminum
nitrate, silicon nitrate, potassium nitrate, calcium nitrate,
titanium nitrate, vanadium nitrate, chromium nitrate, manganese
nitrate, iron nitrate, cobalt nitrate nickel nitrate, copper
nitrate, zinc nitrate, gallium nitrate, germanium nitrate,
zirconium nitrate, palladium nitrate, silver nitrate, cadmium
nitrate, tin nitrate, barium nitrate, hafnium nitrate, tungsten
nitrate, lead nitrate, or the like. In some embodiments, the
precursor is a metal alkoxide (e.g., a methoxide, ethoxide,
isopropyl oxide, t-butyl oxide, or the like). In specific
embodiments, the precursor is lithium alkoxide, beryllium alkoxide,
sodium alkoxide, magnesium alkoxide, aluminum alkoxide, silicon
alkoxide, potassium alkoxide, calcium alkoxide, titanium alkoxide,
vanadium alkoxide, chromium alkoxide, manganese alkoxide, iron
alkoxide, cobalt alkoxide nickel alkoxide, copper alkoxide, zinc
alkoxide, gallium alkoxide, germanium alkoxide, zirconium alkoxide,
palladium alkoxide, silver alkoxide, cadmium alkoxide, tin
alkoxide, barium alkoxide, hafnium alkoxide, tungsten alkoxide,
lead alkoxide, or the like. In some embodiments, the precursor is a
metal halide (e.g., chloride, bromide, or the like). In specific
embodiments, the precursor is lithium halide, beryllium halide,
sodium halide, magnesium halide, aluminum halide, silicon halide,
potassium halide, calcium halide, titanium halide, vanadium halide,
chromium halide, manganese halide, iron halide, cobalt halide
nickel halide, copper halide, zinc halide, gallium halide,
germanium halide, zirconium halide, palladium halide, silver
halide, cadmium halide, tin halide, barium halide, hafnium halide,
tungsten halide, or the like. In certain embodiments, the precursor
is a diketone (e.g., acetylacetone, hexafluoroacetylacetone, or the
like). In specific embodiments, the precursor is lithium diketone,
beryllium diketone, sodium diketone, magnesium diketone, aluminum
diketone, silicon diketone, potassium diketone, calcium diketone,
titanium diketone, vanadium diketone, chromium diketone, manganese
diketone, iron diketone, cobalt diketone nickel diketone, copper
diketone, zinc diketone, gallium diketone, germanium diketone,
zirconium diketone, palladium diketone, silver diketone, cadmium
diketone, tin diketone, barium diketone, hafnium diketone, tungsten
diketone, lead diketone, or the like.
[0172] In some embodiments, the precursor comprises mixtures or
combinations of precursors. In some embodiments, mixtures of metal
precursors are used to form metal alloy nanofibers. In some
embodiments, metal alloy nanofibers are made from precursors that
are alloys of metal. Exemplary metal alloys include CdSe, CdTe,
PbSe, PbTe, FeNi (perm alloy), Fe--Pt intermetallic compound,
Pt--Pb, Pt--Pd, Pt--Bi, Pd--Cu, and Pd--Hf.
Ligands
[0173] As discussed herein, metal precursors used herein generally
comprise a metal in association with a ligand. Ligands are
associated with the metal in any suitable way, such as through
ionic, covalent, coordination complexes, conjugation, or any other
suitable association.
[0174] In some embodiments, precursor molecules do not have a high
solubility in the fluid stock (e.g., optionally not a high
solubility in an aqueous fluid stock). In some instances, a poor
solubility of precursor may make it difficult to achive (a) an
increased weight ratio of precursor in the fluid stock and (b) a
substantially uniform distribution of precursor in the fluid stock.
In some embodiments, the precursor is solubilized. In some
embodiments, the precursor molecules comprise a metal atom in
association with a solvating molecule (i.e., a ligand that improves
the solubility and/or dispersibility of the metal precursor in the
fluid medium, e.g., water). In some embodiments, the a first
precursor may be added to a fluid (e.g., water), but forms a second
precursor in the fluid (e.g., a solvate and/or an association with
a polymer of the fluid stock). Optionally, the solvating molecule
is substantially similar to the monomers of the polymer (e.g.,
ligand is acetate and polymer is polyvinyl acetate). In some
embodiments (e.g., where the polymer is soluble in the fluid
stock), solubility and uniform distribution of the precursor is
achieved by associating the solvating molecule to both the
precursor and the polymer.
[0175] In some embodiments, the solvating molecule is a ligand. The
ligand is suitable for solubilizing or improving the dispersibility
of a metal, optionally in an aqueous solution, optionally in the
fluid stock. The present disclosure includes achieving a more
uniform fluid stock by first solubilizing or distributing the
precursor in a first solution. In some embodiments, the solvating
molecule or ligand also improves the solubility or dispersibility
of the precursor in a first fluid (e.g., dispersion or solution)
(i.e., that is mixed with at least one second solution to make a
fluid stock).
[0176] Some embodiments comprise solubilizing the precursor by
associating a metal with a ligand, optionally complexing the metal
with a ligand. In some embodiments, the precursor comprises a
metal-ligand association (e.g., complex), as discussed herein. In
some instances, the ligands are referred to herein as "molecules"
in association with the metal. The association between the metal
and ligand or molecules is optionally being a chemical bond (e.g.,
covalent bond), ionic bond, conjugation, or coordination complex.
In some embodiments, the precursor is a metal-ligand complex.
[0177] The association between the solvating molecule or ligand and
the precursor is any physical, chemical, or electromagnetic force
known in the art of chemistry. An example of an association is a
chemical bond. Examples of bonds are covalent bonds, non-covalent
bonds, ionic bonds, hydrogen bonds, and the like. Further examples
of associations are hydrophilic interactions and hydrophobic
interactions. The skilled practitioner will be aware of many other
types of interactions or associations that may be employed such as
a Lewis acid-Lewis base interaction between the precursor and the
solvating molecule or ligand. In this embodiment, the ligand is
generally the "Lewis base", meaning that it furnishes an electron
pair to share with a Lewis acid.
[0178] In some embodiments, the association is a metal-ligand
coordination complex. Metal-ligand coordination complexes are also
known as "metal complexes" or "chelation complexes". These
complexes generally include a central atom or ion (usually
metallic), bonded to a surrounding array of molecules or anions,
which in turn are known as ligands or complexing agents. In nature,
most compounds containing metals consist of coordination complexes.
The association between the metal and ligand is strong or weak in
various embodiments.
[0179] There are any suitable number of ligands per metal atom
(e.g., optionally a number suitable to solvate, i.e., increase
solubility or dispersibility of, the metal). The number of ligands
per metal atom is referred to as the "coordination number". In some
embodiments, the coordination numbers is between two and nine (for
ML.sub.b compounds, the coordination number is b). Large numbers of
ligands are not uncommon for the lanthanides and actinides. In
various embodiments, the number of bonds depends on the size,
charge, and electron configuration of the metal ion and the
ligands. Metal ions may have more than one coordination number
(e.g., depending on oxidation state of the metal).
[0180] In some examples there are at least 2 ligand molecules for
every metal atom. In other examples, there are at least 3 ligands
per metal atom. In some embodiments, the precursor is essentially
saturated with ligand. One may determine if the precursor is
essentially saturated with ligand by titrating successively more
ligand into the metal and determining the amount of ligand
complexed by any suitable method known to those in the art of
analytical chemistry. In some embodiments, one determines if the
precursor is essentially saturated with ligand by waiting
successively longer times and determining the amount of ligand
complexed by any suitable method known to those in the art of
analytical chemistry. In some instances, it may be determined that
the precursor is substantially saturated when no more ligand
complexes with the metal precursor at successively higher amounts
of ligand or at successively longer times.
[0181] In one example, the ligand is acetate. In some embodiments,
the precursor molecules are metal acetates and the polymer is
polyvinyl acetate. In another embodiment, the precursor molecules
are metal acetates and the polymer is polyvinyl alcohol.
[0182] There are many ligands known to those skilled in the art,
any of which are utilized. In some embodiments, a precursor
described herein comprises one or more ligand selected from the
group consisting of ketones, diketones (e.g., a 1,3-diketone, such
as ROCCHR'COR group, wherein R is an alkyl, substituted alkyl,
aryl, substituted aryl and R' is R or H), carboxylates (e.g.,
acetate or --OCOR group, wherein each R is independently an alkyl,
substituted alkyl, aryl, substituted aryl), halides, nitrates,
amines (e.g., NR'.sub.3, wherein each R'' is independently R or H
or two R'', taken together form a heterocycle or heteroaryl), and
combinations thereof. Further examples include iodide, bromide,
sulfide (e.g., --SR), thiocyanate, chloride, nitrate, azide,
fluoride, hydroxide, oxalate, water, nitrite (e.g., RN.sub.3),
isothiocyanate, acetonitrile, pyridine, ammonia, ethylenediamine,
2,2'-bipyridine, 1,10-phenanthroline, nitrite, triphenylphosphate,
cyanide, carbon monoxide, or alko-oxide. In some examples, the
precursor is a metal complex such as metal acetate, metal halide
(e.g., metal chloride), metal nitrate, or metal alko-oxide (e.g.,
methoxide or ethoxide).
[0183] In various embodiments, metal and/or ceramic precursors are
metal atoms associated (complexed) with a ligand. Exemplary metal
and/or ceramic precursors include nickel acetate, copper acetate,
iron acetate, nickel nitrate, copper nitrate, iron alko-oxide, and
the like.
[0184] The present disclosure also encompasses the use of
combinations of ligands. In one example, a first ligand imparts
increased solubility to the precursor, while a second ligand
preferentially associates with the polymer.
Polymers
[0185] In some embodiments, a polymer described herein (e.g., in a
process, precursor nanofiber, a fluid stock, or the like) is a
polymer (e.g., homopolymer or copolymer) comprising a plurality of
reactive sites. In certain embodiments, the reactive sites are
nucleophilic (i.e., a nucleophilic polymer) or electrophilic (i.e.,
an electrophilic polymer). For example, in some embodiments, a
nucleophilic polymer described herein comprises a plurality of
alcohol groups (such as polyvinyl alcohol--PVA--or a cellulose),
ether groups (such as polyethylene oxide--PEO--or polyvinyl
ether--PVE), and/or amine groups (such as polyvinyl pyridine,
((di/mono)alkylamino)alkyl alkacrylate, or the like).
[0186] In some embodiments, provided herein are fluid stocks
comprising and/or methods comprising electrospinning a fluid stock
comprising a polymer. The methods described herein optionally
utilize an aqueous fluid stock. In some applications, a water-based
process is desirable, for instance if one wants to avoid potential
health, environmental, or safety problems associated with organic
solvents. As described herein, in some embodiments it is
advantageous to electrospin a fluid stock that is homogenous. In
some embodiments, the fluid stock is homogenous (e.g., which
comprises a water-soluble polymer).
[0187] In some embodiments, polymers used in the compositions and
processes described herein are hydrophilic polymers, including
water-soluble and water swellable polymers. In some aspects, the
polymer is soluble in water, meaning that it forms a solution in
water. In other embodiments, the polymer is swellable in water,
meaning that upon addition of water to the polymer the polymer
increases its volume up to a limit. Water soluble or swellable
polymers are generally at least somewhat hydrophilic. Exemplary
polymers suitable for the present methods include but are not
limited to polyvinyl alcohol ("PVA"), polyvinyl acetate ("PVAc"),
polyethylene oxide ("PEO"), polyvinyl ether, polyvinyl pyrrolidone,
polyglycolic acid, hydroxyethylcellulose ("HEC"), ethylcellulose,
cellulose ethers, polyacrylic acid, polyisocyanate, and the like.
In some embodiments, the polymer is isolated from biological
material. In some embodiments, the polymer is starch, chitosan,
xanthan, agar, guar gum, and the like.
[0188] In some embodiments, the polymer imparts a suitable
elongational viscosity to the fluid stock for electrospinning
nanofibers. In some embodiments, low shear viscosity leads to
beaded nanofibers. In one aspect, uniform distribution of the
precursor in the fluid feed helps to maintain a suitably high
elongational viscosity.
[0189] Viscosity is a measure of the resistance of a fluid which is
being deformed by either shear stress or tensile stress. Viscosity
is measured in units of poise. In various embodiments, the
viscosity of the polymer or fluid stock is measured with or without
associated precursor. The polymer or fluid stock has any suitable
elongational viscosity. In some embodiments, the polymer or fluid
stock has an elongational viscosity of about 10 poise, 50 poise,
about 100 poise, about 200 poise, about 300 poise, about 400 poise,
about 500 poise, about 600 poise, about 800 poise, about 1000
poise, about 1500 poise, about 2000 poise, about 2500 poise, about
3000 poise, about 5,000 poise, and the like. In some embodiments,
the polymer or fluid stock has an elongational viscosity of at
least 50 poise, at least 100 poise, at least 200 poise, at least
300 poise, at least 400 poise, at least 500 poise, at least 600
poise, at least 800 poise, at least 1,000 poise, at least 1,500
poise, at least 2,000 poise, at least 2,500 poise, at least 3,000
poise, at least 5,000 poise, and the like. In some embodiments, the
polymer or fluid stock has an elongational viscosity of at most 50
poise, at most 100 poise, at most 200 poise, at most 300 poise, at
most 400 poise, at most 500 poise, at most 600 poise, at most 800
poise, at most 1,000 poise, at most 1,500 poise, at most 2,000
poise, at most 2,500 poise, at most 3,000 poise, at most 5,000
poise, and the like. In some embodiments, the polymer or fluid
stock has an elongational viscosity of between about 100 and 3,000
poise, or between about 1,000 and 5,000 poise, and the like.
[0190] Molecular weight is related to the mass of the monomers
comprising the polymer and the degree of polymerization. In some
embodiments, molecular weight is a factor that affects viscosity.
The polymer has any suitable molecular weight. In some embodiments,
the polymer has a molecular weight of at least 20,000 atomic mass
units ("amu"), at least 50,000 amu, at least 100,000 amu, at least
200,000 amu, at least 300,000 amu, at least 400,000 amu, at least
500,000 amu, at least 700,000 amu, or at least 1,000,000 amu and
the like. In some embodiments, the polymer has a molecular weight
of at most 20,000 amu, at most 50,000 amu, at most 100,000 amu, at
most 200,000 amu, at most 300,000 amu, at most 400,000 amu, at most
500,000 amu, at most 700,000 amu, or at most 1,000,000 amu and the
like. In some embodiments, the polymer has a molecular weight of
about 20,000 amu, about 50,000 amu, about 100,000 amu, about
200,000 amu, about 300,000 amu, about 400,000 amu, about 500,000
amu, about 700,000 amu, or about 1,000,000 amu and the like. In yet
other embodiments, the polymer has a molecular weight of from about
50,000 amu to about 1,00,000 amu, from about 100,000 amu to about
500,000 amu, from about 200,000 amu to about 400,000 amu, or from
about 500,000 amu to about 1,00,000 amu and the like.
[0191] The polydispersity index ("PDI") is a measure of the
distribution of molecular mass in a given polymer sample. The PDI
is the weight average molecular weight divided by the number
average molecular weight, which is calculated by formula known to
those skilled in the art of polymer science. The polymer has any
suitable polydispersity index. In some embodiments, the polymer has
a polydispersity index of about 1, about 2, about 3, about 4, about
5, about 6, about 7, about 8, about 9, about 10, about 15, about
20, and the like. In some embodiments, the polymer has a
polydispersity index of at least 1, at least 2, at least 3, at
least 4, at least 5, at least 6, at least 7, at least 8, at least
9, at least 10, at least 15, at least 20, and the like. In some
embodiments, the polymer has a polydispersity index of at most 1,
at most 2, at most 3, at most 4, at most 5, at most 6, at most 7,
at most 8, at most 9, at most 10, at most 15, at most 20, and the
like. In some embodiments, the polymer has a polydispersity index
of about 1 to about 10, about 2 to about 5, and the like.
[0192] The present disclosure includes polymers, includes polymers
having the characteristic herein disclosed, includes polymers
prepared according to the methods herein disclosed, includes
polymers preparable by the methods herein disclosed, includes
polymers incorporating the precursor herein disclosed, and includes
polymers suitable for the methods and systems herein disclosed. The
present disclosure also includes methods for using the polymers,
and the like.
[0193] In some embodiments, the fluid stock comprises mixtures or
combinations of polymers. For example, in some embodiments, a first
polymer binds to a first precursor and a second polymer binds to a
second precursor (e.g., to form a composite nanofiber following
treatment of the precursor nanofiber). In another example, a first
polymer associates with a high amount of precursor and a second
polymer is chosen to create high quality nanofibers when
electrospun (e.g., elongational viscosity). In some embodiments,
the fluid stock includes a high-precursor loading polymer and a
highly spinnable polymer.
[0194] In some embodiments, the fluid stock comprises co-polymers
including block co-polymers. In some embodiments, the co-polymer
comprises at least one vinylalcohol, vinylpyrrolidone,
vinylacetate, ethylene oxide, dimethylacrylamide, and/or
polyacrylamide block. In some embodiments, the various blocks of
the co-polymer associate with different precursors. In one example,
a first polymer block associates with nickel precursor and a second
polymer block associates with iron precursor (e.g., to form a
composite nanofiber following treatment of a precursor nanofiber
that has nano-domains of nickel interspersed with nano-domains of
iron corresponding to the distribution of the blocks of their
respective polymer associations). In some embodiments, such a
nanofiber has different properties than a nickel-iron alloy
nanofiber (i.e., where the nickel and iron are substantially
uniformly mixed on the molecular level). In some embodiments,
provided herein is a nanocomposite nanofiber comprising a first
material and a second material. In specific embodiments, the first
material is a continuous matrix material. In further or alternative
embodiments, the second material makes up discrete, isolated
domains of the nanofiber (e.g., on the surface of the nanofiber).
In some embodiments, the first material is a ceramic or metal oxide
(e.g., forming a continuous matrix). In certain embodiments, the
second material is a metal.
[0195] In some embodiments, the polymer is removed from the
nanofiber following electrospinning (e.g., by the calcination
methods herein disclosed). In some embodiments, calcination
degrades the polymer. In some embodiments, the fluid stock
comprises degradable polymers (e.g., polymers removable by the
calcination methods herein disclosed). The polymer is optionally
degraded or removed by any suitable means including, but not
limited to thermal degradation, chemical degradation, sublimation,
evaporation, and the like. In some embodiments, lower molecular
weight polymers are easier to remove by evaporation or
sublimation.
Polymer-Precursor Associations
[0196] In some embodiments, associating the precursor with the
polymer achieves at least one of a high proportion of precursor in
the fluid stock and a uniform distribution of precursor in the
fluid stock. In some instances the association reduces the amount
of voids or defects in the nanofiber. In some embodiments,
associating the precursor with the polymer increases the solubility
of one or more of the precursor and the polymer in the fluid stock.
The present disclosure encompasses precursor in association with
polymer and encompasses methods for associating precursor with
polymer.
[0197] In some instances, a moiety (e.g., a hydroxyl, amine, ether,
etc.) of the polymer may displace and replace a ligand of the
precursor (i.e., converting a first precursor to a second
precursor). In other instances, a moiety of the polymer may react
directly with the ligand (e.g., a nucleophilic group of a polymer
may react with an electrophilic group of the ligand, or vis versa).
FIG. 2A illustrates one mechanism by which a polymer may be
associated with a precursor.
[0198] In some embodiments, the precursor associates with the
polymer in the fluid stock. In some embodiments, the process
described herein utilizes an association of the precursor with the
polymer to provide a fluid stock wherein precursor is uniformly
distributed in the fluid stock. In various embodiments, the fluid
stock remains a solution or substantially uniform dispersion (e.g.,
in part because the precursor associates with the polymer in the
fluid stock). In various embodiments, the association is a
physical, chemical, or electromagnetic force between the precursor
and the polymer. Examples of associations are chemical bonds.
Examples of bonds are covalent bonds, non-covalent bonds, ionic
bonds, hydrogen bonds, and the like. Further examples of
associations are hydrophilic interactions and hydrophobic
interactions. Other types of suitable interactions or associations
are a Lewis acid-Lewis base interaction between the precursor and
the polymer. In some embodiments, the association is a metal-ligand
complex.
[0199] In some embodiments, the monomers along the polymer chain
provide sites to which precursor associates. In some embodiments,
these sites are chemical groups including but not limited to
hydroxyl groups, carbonyl groups, aldehyde groups, esters, amines,
coarboxyamide, imines, nitrates and the like. In some embodiments,
groups contain hydrocarbons, halogens, oxygen, nitrogen, sulfur,
phosphorus and the like. Those skilled in the art will be familiar
with chemical groups. Chemical groups are also known as "functional
groups". In some embodiments, precursors associate with chemical
groups on the polymer through chemical bonds.
[0200] In some aspects, the polymer comprises a plurality of
moieties. In some embodiments, these moieties are chemical groups,
optionally chemical groups of the monomers bound along the polymer
chain. In some embodiments, the moieties complex or bind with
precursors, including metals. In some embodiments, the moieties
displace the ligand of a metal-ligand precursor. In some
embodiments, the polymer includes on average at least 100
functional groups, chemical groups, or moieties per polymer
molecule that are capable of associating with a precursor (e.g.,
optionally with a metal precursor).
[0201] In one example, the precursors are iron acetates (a metal
ligand complex) and the polymer is polyvinyl alcohol. In this
example, the moiety or functional group is an alcohol group. The
polymer has a plurality of alcohol groups along its backbone
suitable for associating with the iron acetate. In this example,
the acetate either binds to the alcohol groups while still being
complexed with the iron, or the alcohol groups displace the acetate
ligand and associate directly with the iron.
[0202] In some embodiments, the amount of precursor associated or
loaded onto the polymer is high. In some embodiments, higher
loading is related to the number of functional groups in the
polymer (which depends in part on the molecular weight of the
polymer and concentration of the functional groups). In some
instances, more functional groups provide more sites for precursor
to associate, thereby enabling higher precursor loading.
[0203] In some instances, the quantity of precursor associated with
the polymer is determined at least in part by the number of ligands
per precursor. In some embodiments, more ligands per metal increase
the probability of a ligand associating with a functional group on
the polymer. In one example, there are three acetate ligands per
aluminum in the precursor.
[0204] In some embodiments, the polymer is essentially saturated
with precursor molecules, meaning that substantially no more
precursors will associate with the polymer. In some embodiments,
the saturation is determined by adding an excess of precursor to
the polymer, separating the polymer from the precursor and
determining what quantity of precursor bound to the polymer. The
amount of precursor is measured using any suitable technique known
in the art of analytical chemistry. In some instances, following
separation, the practitioner determines the amount of unassociated
precursor, the amount precursor associated with the polymer, or
both the amount of unassociated precursor and the amount precursor
associated with the polymer. Tests of this nature are conducted
with progressively more precursor added to the fluid stock until no
more precursor binds to the polymer, indicating that the precursor
is present in excess amount and the polymer is saturated. In some
instances, measurements are conducted over progressively longer
time periods of contact between the precursor and the polymer to
verify that no more precursor associates with the polymer at longer
times, and the polymer is saturated with precursor. Another
suitable method for determining saturation is to calculate the
stoichiometry of the association. For example in some instances,
one compares the moles of chemical groups on the polymer in the
fluid stock and the moles of precursor molecules associated with
those functional groups. If one precursor associates with one
chemical group, the polymer is saturated when the moles of
precursor is substantially equal to the moles of chemical
groups.
[0205] In some embodiments, the polymer is saturated with precursor
up to any suitable level. In some instances, various samples of
polymer have a distribution of precursor saturation levels.
Individual polymer samples accordingly exceed or fall short of the
average precursor saturation. In some embodiments, the polymer is
on average less than 100% saturated with precursor. For example,
the polymer is on average at least 20%, at least at least 30%, at
least 40%, at least 50%, at least 60%, at least 70%, at least 75%,
at least 80%, at least 85%, at least 85%, at least 90%, at least
95%, at least 96%, at least 97%, at least 98%, or at least 99%
saturated. In some instances, the polymer is on average between
about 50% and 100%, between about 70% and 100%, between about 90%
and 100%, between about 50% and 90%, between about 60% and 80%, or
between about 20% and 50% saturated.
[0206] For the purposes of this disclosure, it is to be understood
that reference to a polymer type (e.g., PVA) is intended to include
such a polymer when not associated with precursor as well as when
associated with precursor (in those cases where the polymer is
associated with precursor, the polymer refers to the polymer
residue that remains following the reaction/association). For
example, in instances where PVA is combined with a precursor
ML.sub.b, reference to PVA includes reference to unassociated
polymer of the P--OH type (including partially or completely
ionized forms), and the associated P--O-ML.sub.b-1 type (wherein
the reference to "PVA" refers to the P--O portion and the
ML.sub.b-1 refers to a precursor that may be present to the
exclusion of ML.sub.b or in addition to ML.sub.b, depending on the
extent to which the ML.sub.b precursor is loaded upon or associated
with the PVA).
Nanofibers
[0207] Provided in certain embodiments herein are nanofibers, e.g.,
nanofibers having any one or more of the characteristics herein
disclosed, nanofibers prepared according to the methods described
herein, and nanofibers preparable by the methods described herein.
Also provided herein are processes for using the nanofibers,
devices comprising the nanofibers and the like.
[0208] In some embodiments, the nanofibers have few defects and/or
voids. In some instances a voids and defects in the nanofiber
include breaks in the nanofiber, regions of nanofiber wherein the
diameter is so narrow as to be easily broken (e.g., having a
diameter of less than 10% or less than 5% of the average nanofiber
diameter), regions of the nanofiber wherein the nanofiber material
has anomalous morphologies (e.g., crystalline domains in a
substantially amorphous nanofiber--such crystalline domains may
increase fracturing and brittleness of the nanofiber), and the
like. In some embodiments, there are about 1, about 5, about 10,
about 50, about 100, and the like defects per linear mm of
nanofiber. In some embodiments, there are at most about 1, at most
about 5, at most about 10, at most about 50, at most about 100, and
the like defects per linear mm of nanofiber. In other embodiments,
the nanofibers have fewer defects and/or voids, wherein the number
of defects and/or voids in the nanofiber is in comparison to a
nanofiber not produced by the methods of the disclosure (for
example with a low loading of precursor).
[0209] Metal Nanofibers
[0210] Provided in various embodiments herein are pure metal
nanofibers, nanofibers comprising metal, or nanofibers
substantially comprised of metal. Pure metal nanofibers have any
suitable percent composition of metal. In some embodiments, a metal
nanofiber provided herein comprises about 99.99%, about 99.95%,
about 99.9%, about 99%, about 98%, about 97%, about 96%, about 95%,
about 90%, about 80%, and the like of metal by mass. In some
embodiments, the metal nanofiber comprises at least about 99.99%,
at least about 99.95%, at least about 99.9%, at least about 99%, at
least about 98%, at least about 97%, at least about 96%, at least
about 95%, at least about 90%, at least about 80%, and the like of
metal by mass (e.g., elemental mass). In other embodiments, metal
nanofibers provided herein comprise at least 50%, at least 60%, at
least 70%, or at least 75% metal by mass (e.g., elemental mass). In
specific embodiments, metal nanofibers provided herein comprise at
least 80% metal by mass. In more specific embodiments, metal
nanofibers provided herein comprise at least 90% metal by mass. In
still more specific embodiments, metal nanofibers provided herein
comprise at least 95% metal by mass.
[0211] In certain embodiments, metal nanofibers provided herein
comprise a continuous matrix of crystalline metal. In some
instances, the continuous matrix of crystalline metal, with few or
no defects, provides for improved performance of the metal
nanofibers (e.g., improved electrical conductivity).
[0212] In some embodiments, the metal nanofibers comprise a single
metal. In other embodiments, the metal nanofibers comprise two or
more metals. In some embodiments, provided herein are metal
nanofibers comprising two or more metals and the metals are in the
form of an alloy. In other embodiments, provided herein are metal
nanofibers comprising two or more metals and the metals are in the
form of a composite (e.g., a layered hybrid nanofiber, a composite
with distinct metal segments, a composite with a first metal that
forms a continuous matrix and a second metal that is present in
isolated domains within the nanofiber, or the like).
[0213] In some embodiments, metal nanofibers provided herein
comprises less than 10% carbon by mass (e.g., elemental mass). In
certain embodiments, metal nanofibers provided herein comprise less
than 7% carbon by mass. In specific embodiments, metal nanofibers
provided herein comprise less than 5% carbon by mass. In more
specific embodiments, metal nanofibers provided herein comprise
less than 3% carbon by mass. In still more specific embodiments,
metal nanofibers provided herein comprise less than 1% carbon by
mass. In some embodiments, metal nanofibers provided herein
comprises less than 5% oxygen by mass (e.g., elemental mass). In
certain embodiments, metal nanofibers provided herein comprise less
than 3% oxygen by mass. In specific embodiments, metal nanofibers
provided herein comprise less than 2% oxygen by mass. In more
specific embodiments, metal nanofibers provided herein comprise
less than 2% oxygen by mass. In still more specific embodiments,
metal nanofibers provided herein comprise less than 0.5% oxygen by
mass.
[0214] FIG. 15 illustrates the elemental analysis of nickel
nanofibers prepared according to a process herein. In both light
and dark regions (panels A and B, respectively) of the nanofiber,
the nanofiber is observed to have high nickel content. The
elemental ratios of nickel to oxygen to carbon were about 64:1:0.25
in the dark region and 62:5:0.1 in the light region.
[0215] The metal is any metal, including: transition metal, alkali
metal, alkaline earth metal, post-transition metal, lanthanide, or
actinide. Suitable transition metals include: scandium (Sc),
titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron
(Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), yttrium
(Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium
(Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag),
cadmium (Cd), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium
(Re), osmium (Os), iridium (Ir), platinum (Pt), gold (Au), mercury
(Hg), rutherfordium (Rf), dubnium (Db), seaborgium (Sg), bohrium
(Bh), and hasium (Hs). Suitable alkali metals include: lithium
(Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs) and
francium (Fr). Suitable alkaline earth metals include: beryllium
(Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba),
and radium (Ra). Suitable post-transition metals include: aluminum
(Al), gallium (Ga), indium (In), tin (Sn), thallium (Tl), lead
(Pb), and bismuth (Bi). Suitable lanthanides include the elements
with atomic number 57 to 71 on the periodic table. Suitable
actinides include the elements with atomic number 89 to 103 on the
periodic table. In some embodiments, the nanofiber is germanium
(Ge), antimony (Sb) and polonium (Po), or silicon (Si). By way of
non-limiting example, certain methods for producing metal
nanofibers are disclosed herein and optionally include calcination
under reducing conditions.
[0216] In specific embodiments, nanofiber comprises an alkali
metal. In further or alternative embodiments, the nanofiber
comprises an alkaline earth metal. In certain embodiments, the
nanofiber comprises a transition metal. In some embodiments, the
nanofiber comprises a period IV transition metal. In certain
embodiments, the nanofiber comprises a period V transition metal.
In some embodiments, the nanofiber comprises a group XIII metal. In
certain embodiments, nanofiber comprises is a group XIV metal. In
certain embodiments, the nanofiber comprises a metalloid. In
specific embodiments, the nanofiber comprises lithium, beryllium,
sodium, magnesium, aluminum, silicon, potassium, calcium, titanium,
vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc,
gallium, germanium, zirconium, palladium, silver, cadmium, tin,
barium, hafnium, tungsten, lead, combinations thereof, or the like.
In specific embodiments, the nanofiber comprises silicon.
[0217] FIGS. 3, 5, 7, 8, 12, 22, 23, 26, 27, and 28 illustrate
precursor and metal nanofibers provided herein and/or as prepared
according to the processes described herein. FIG. 3 illustrates
nickel precursor nanofibers 301 having average diameters of 500-700
nm, and nickel nanofibers 302, having average diameters of 400-500
nm, prepared from the nickel precursor nanofibers 301 after
treatment at 600.degree. C. for 2 hours in Argon. FIG. 3 also
illustrates the crystal x-ray diffraction pattern 303 of the nickel
nanofibers 302. FIG. 5 illustrates copper precursor nanofibers 501
having average diameters of 600-800 nm, and copper nanofibers 502,
having average diameters of 300-500 nm, prepared from the copper
precursor nanofibers 501 after treatment at 800.degree. C. for 2
hours in a Argon/Hydrogen mixture. FIG. 5 also illustrates the
crystal x-ray diffraction pattern 503 of the copper nanofibers 502.
FIG. 7 illustrates silver precursor nanofibers 701 having average
diameters of 900-1200 nm, and silver nanofibers 702, having average
diameters of 600-800 nm, prepared from the silver precursor
nanofibers 701 after treatment at 600.degree. C. for 2 hours in
air. FIG. 7 also illustrates the crystal x-ray diffraction pattern
703 of the silver nanofibers 702. FIG. 8 illustrates iron precursor
nanofibers 801 having average diameters of 300-600 nm, and iron
nanofibers 802, having average diameters of 200-500 nm, prepared
from the iron precursor nanofibers 801 after treatment at
600.degree. C. for 2 hours in argon. FIG. 8 also illustrates the
crystal x-ray diffraction pattern 803 of the iron nanofibers 802.
FIG. 12 illustrates lead precursor nanofibers 1201 having average
diameters of 500-1100 nm, and lead nanofibers 1202, having average
diameters of 250-700 nm, prepared from the lead precursor
nanofibers 1201 after treatment at 600.degree. C. for 2 hours in an
argon/hydrogen mixture. FIG. 12 also illustrates the crystal x-ray
diffraction pattern 1203 of the lead nanofibers 1202. FIG. 13
illustrates nickel precursor nanofibers (Panel B) and nickel
nanofibers (Panel D). Depending on the precursor loading (Panel A),
based on the weight-to-weight ratio of nickel acetate and PVA
combined into a fluid stock, different diameters of precursor
nanofibers (Panel C) and metal nanofibers (Panel E) were obtained.
FIG. 14 also illustrates nickel nanofibers prepared from fluid
stocks prepared from nickel acetate and PVA (Panel A illustrates
the loading based on the weight-to-weight ratio of
polymer-to-precursor). FIG. 15 illustrates an elemental analysis of
metal nanofibers prepared according to the instant disclosure.
FIGS. 22 and 23 illustrate metal alloy nanofibers prepared
according to the instant disclosure. FIG. 22 illustrates
cadmium-selenium precursor nanofibers 2201 having average diameters
of 300-1000 nm, and cadmium-selenium alloy nanofibers 2202, having
average diameters of 500-700 nm, prepared from the cadmium-selenium
precursor nanofibers 2201 after treatment at 600.degree. C. for 2
hours in argon. FIG. 22 also illustrates the crystal x-ray
diffraction pattern 2203 of the cadmium-selenium alloy nanofibers
2202. FIG. 23 illustrates lead-selenium precursor nanofibers 2301
having average diameters of 700-1300 nm, and lead-selenium alloy
nanofibers 2302, having average diameters of 600-900 nm, prepared
from the lead-selenium precursor nanofibers 2301 after treatment at
600.degree. C. for 2 hours in argon. FIG. 23 also illustrates the
crystal x-ray diffraction pattern 2303 of the lead-selenium alloy
nanofibers 2302. FIG. 24 illustrates a more zoomed view of the
cadmium-selenium and lead-selenium alloy nanofibers, and FIG. 25
illustrates an elemental analysis of the lead-selenium alloy
nanofibers. FIG. 26 illustrates cadmium-tellurium precursor
nanofibers 2601 having average diameters of 500-900 nm, and
cadmium-tellurium alloy nanofibers 2602, having average diameters
of 300-650 nm, prepared from the cadmium-tellurium precursor
nanofibers 2601 after treatment at 600.degree. C. for 2 hours in
argon. FIG. 26 also illustrates the crystal x-ray diffraction
pattern 2603 of the cadmium-tellurium alloy nanofibers 2602. FIG.
27 illustrates lead-tellurium precursor nanofibers 2701 having
average diameters of 400-700 nm, and lead-tellurium alloy
nanofibers 2702, having average diameters of 300-550 nm, prepared
from the lead-tellurium precursor nanofibers 2701 after treatment
at 600.degree. C. for 2 hours in argon. FIG. 27 also illustrates
the crystal x-ray diffraction pattern 2703 of the lead-tellurium
alloy nanofibers 2702. FIG. 28 illustrates iron-nickel precursor
nanofibers 2801 having average diameters of 600-1000 nm, and
iron-nickel alloy nanofibers 2802, having average diameters of
200-750 nm, prepared from the iron-nickel precursor nanofibers 2801
after treatment at 600.degree. C. for 2 hours in an argon/hydrogen
mixture. FIG. 28 also illustrates the crystal x-ray diffraction
pattern 2803 of the iron-nickel alloy nanofibers 2802. FIG. 29
illustrates TEM images for iron oxide/iron-nickel
Ceramic and Metal Oxide Nanofibers
[0218] Provided in various embodiments herein are pure ceramic
nanofibers, nanofibers comprising ceramic, or nanofibers
substantially comprised of ceramic. In some embodiments, the
ceramic nanofiber comprises about 99.99%, about 99.95%, about
99.9%, about 99%, about 98%, about 97%, about 96%, about 95%, about
90%, about 80%, and the like of ceramic by mass. In some
embodiments, the ceramic nanofiber comprises at least about 99.99%,
at least about 99.95%, at least about 99.9%, at least about 99%, at
least about 98%, at least about 97%, at least about 96%, at least
about 95%, at least about 90%, at least about 80%, and the like of
ceramic by mass (e.g., elemental mass). In other embodiments,
ceramic nanofibers provided herein comprise at least 50%, at least
60%, at least 70%, or at least 75% ceramic by mass (e.g., elemental
mass). In specific embodiments, ceramic nanofibers provided herein
comprise at least 80% ceramic by mass. In more specific
embodiments, ceramic nanofibers provided herein comprise at least
90% ceramic by mass. In still more specific embodiments, ceramic
nanofibers provided herein comprise at least 95% ceramic by
mass.
[0219] Provided in various embodiments herein are pure metal oxide
(including, e.g., metal oxide ceramics) nanofibers, nanofibers
comprising ceramic, or nanofibers substantially comprised of
ceramic. In some embodiments, the metal oxide nanofiber comprises
about 99.9%, about 99%, about 98%, about 97%, about 96%, about 95%,
about 90%, about 80%, and the like of ceramic by mass. In some
embodiments, the metal oxide nanofiber comprises at least about at
least about 99%, at least about 98%, at least about 97%, at least
about 96%, at least about 95%, at least about 90%, at least about
80%, and the like of metal oxide by mass (e.g., elemental mass). In
other embodiments, metal oxide nanofibers provided herein comprise
at least 50%, at least 60%, at least 70%, or at least 75% metal
oxide by mass (e.g., elemental mass). In specific embodiments,
metal oxide nanofibers provided herein comprise at least 80% metal
oxide by mass. In more specific embodiments, metal oxide nanofibers
provided herein comprise at least 90% metal oxide by mass. In still
more specific embodiments, metal oxide nanofibers provided herein
comprise at least 95% metal oxide by mass. In some embodiments,
metal oxide nanofibers provided herein comprise at least 80% metal
and oxygen by mass. In more specific embodiments, metal oxide
nanofibers provided herein comprise at least 90% metal and oxygen
by mass. In still more specific embodiments, metal oxide nanofibers
provided herein comprise at least 95% metal and oxygen by mass. In
yet more specific embodiments, metal oxide nanofibers provided
herein comprise at least 98% metal and oxygen by mass.
[0220] In some embodiments, metal nanofibers provided herein
comprises less than 10% carbon by mass (e.g., elemental mass). In
certain embodiments, metal nanofibers provided herein comprise less
than 7% carbon by mass. In specific embodiments, metal nanofibers
provided herein comprise less than 5% carbon by mass. In more
specific embodiments, metal nanofibers provided herein comprise
less than 3% carbon by mass. In still more specific embodiments,
metal nanofibers provided herein comprise less than 1% carbon by
mass.
[0221] In specific embodiments, the ceramic of a nanofiber provided
herein is a metal oxide. Exemplary ceramics or metal oxides include
but are not limited to Al.sub.2O.sub.3, ZrO.sub.2, Fe.sub.2O.sub.3,
CuO, NiO, ZnO, CdO, SiO.sub.2, TiO.sub.2, V.sub.2O.sub.5, VO.sub.2,
Fe.sub.3O.sub.4, SnO, SnO.sub.2, CoO, CoO.sub.2, Co.sub.3O.sub.4,
HfO.sub.2, BaTiO.sub.3, SrTiO.sub.3, and BaSrTiO.sub.3. Methods for
producing ceramic (and/or metal oxide) nanofibers are disclosed
herein and optionally include calcination under oxidizing
conditions.
[0222] The metal of the metal oxide or ceramic is any metal,
including: transition metal, alkali metal, alkaline earth metal,
post-transition metal, lanthanide, or actinide. Suitable transition
metals include: scandium (Sc), titanium (Ti), vanadium (V),
chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni),
copper (Cu), zinc (Zn), yttrium (Y), zirconium (Zr), niobium (Nb),
molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium (Rh),
palladium (Pd), silver (Ag), cadmium (Cd), hafnium (Hf), tantalum
(Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir),
platinum (Pt), gold (Au), mercury (Hg), rutherfordium (Rf), dubnium
(Db), seaborgium (Sg), bohrium (Bh), and hasium (Hs). Suitable
alkali metals include: lithium (Li), sodium (Na), potassium (K),
rubidium (Rb), cesium (Cs) and francium (Fr). Suitable alkaline
earth metals include: beryllium (Be), magnesium (Mg), calcium (Ca),
strontium (Sr), barium (Ba), and radium (Ra). Suitable
post-transition metals include: aluminum (Al), gallium (Ga), indium
(In), tin (Sn), thallium (Tl), lead (Pb), and bismuth (Bi).
Suitable lanthanides include the elements with atomic number 57 to
71 on the periodic table. Suitable actinides include the elements
with atomic number 89 to 103 on the periodic table. In some
embodiments, the metal of the metal oxide is a metalloid, such as,
germanium (Ge), antimony (Sb) and polonium (Po), or silicon (Si).
By way of non-limiting example, certain methods for producing
ceramic or metal oxide nanofibers are disclosed herein and
optionally include calcination under oxidizing conditions.
[0223] In specific embodiments, nanofiber comprises an oxide of or
ceramic comprising an alkali metal. In further or alternative
embodiments, the nanofiber comprises an oxide of or ceramic
comprising an alkaline earth metal. In certain embodiments, the
nanofiber comprises a transition metal. In some embodiments, the
nanofiber comprises an oxide of or ceramic comprising a period IV
transition metal. In certain embodiments, the nanofiber comprises
an oxide of or ceramic comprising a period V transition metal. In
some embodiments, the nanofiber comprises an oxide of or ceramic
comprising a group XIII metal. In certain embodiments, nanofiber
comprises an oxide of or ceramic comprising is a group XIV metal.
In certain embodiments, the nanofiber comprises an oxide of or
ceramic comprising a metalloid. In specific embodiments, the
nanofiber comprises an oxide of or ceramic comprising aluminum,
silicon, calcium, titanium, vanadium, chromium, manganese, iron,
cobalt, nickel, copper, zinc, gallium, germanium, zirconium,
cadmium, tin, barium, hafnium, tungsten, lead, combinations
thereof, or the like. In specific embodiments, the oxide is not an
oxide of silicon, zirconium, or aluminum. In some embodiments, the
oxide is an oxide of silicon, zirconium, or aluminum, and further
comprises an additional material (e.g., a metal, metal alloy, or
the like), such as in a composite material (e.g., a layered hybrid
nanofiber, a composite with distinct segments, a composite with a
first material that forms a continuous matrix and a second material
that is present in isolated domains within the nanofiber--e.g.,
wherein the oxide is the matrix material, or the like).
[0224] In some embodiments, the ceramic and metal oxide nanofibers
comprise a single metal type. In other embodiments, the ceramic and
metal oxide nanofibers comprise a two or more metal types (e.g.,
BaTiO3, SrTiO3, BaSrTiO3 (e.g., Ba0.55Sr0.45TiO3), and the like).
In some embodiments, provided herein are ceramic and metal oxide
nanofibers comprising two or more metal types together form a
multi-metal oxide or in an ordered alloy type crystalline lattice.
In other embodiments, the two or more metal types form separate
oxide materials in an amorphous mixture, in a composite (e.g., a
layered hybrid nanofiber, a composite with distinct oxide segments,
a composite with a first material that forms a continuous matrix
and a second material that is present in isolated domains within
the nanofiber, or the like), or the like.
[0225] FIGS. 4, 6, 9, 10, and 11 illustrate metal precursor and
metal oxide (e.g., metal oxide ceramic) nanofibers provided herein
and/or as prepared according to the processes described herein.
FIG. 4 illustrates nickel precursor nanofibers 401 having average
diameters of 500-700 nm, and nickel oxide nanofibers 402, having
average diameters of 300-500 nm, prepared from the nickel precursor
nanofibers 401 after treatment at 600.degree. C. for 2 hours in
air. FIG. 4 also illustrates the crystal x-ray diffraction pattern
403 of the nickel oxide nanofibers 402. FIG. 6 illustrates copper
precursor nanofibers 601 having average diameters of 600-800 nm,
and copper oxide nanofibers 602, having average diameters of
200-600 nm, prepared from the copper precursor nanofibers 601 after
treatment at 600.degree. C. for 2 hours in air. FIG. 6 also
illustrates the crystal x-ray diffraction pattern 603 of the copper
oxide nanofibers 602. FIG. 9 illustrates zinc precursor nanofibers
901 having average diameters of 500-1000 nm, and zinc oxide
nanofibers 902, having average diameters of 400-700 nm, prepared
from the zinc precursor nanofibers 901 after treatment at
600.degree. C. for 2 hours in air. FIG. 9 also illustrates the
crystal x-ray diffraction pattern 903 of the zinc oxide nanofibers
902. FIG. 10 illustrates cadmium precursor nanofibers 1001 having
average diameters of 800-1200 nm, and cadmium oxide nanofibers
1002, having average diameters of 600-900 nm, prepared from the
cadmium precursor nanofibers 1001 after treatment at 800.degree. C.
for 2 hours in air. FIG. 10 also illustrates the crystal x-ray
diffraction pattern 1003 of the cadmium oxide nanofibers 1002. FIG.
11 illustrates zirconium precursor nanofibers 1101 having average
diameters of 800-1000 nm, and zirconia nanofibers 1102, having
average diameters of 300-600 nm, prepared from the zirconium
precursor nanofibers 1101 after treatment at 800.degree. C. for 2
hours in air. FIG. 11 also illustrates the crystal x-ray
diffraction pattern 1103 of the zirconia nanofibers 1102.
[0226] Alloy Nanofibers
[0227] Provided in various embodiments herein are pure metal alloy
nanofibers, nanofibers comprising metal alloy, or nanofibers
substantially comprised of metal alloy. The metal alloy is any
suitable metal alloy including: transition metal, alkali metal,
alkaline earth metal, post-transition metal, lanthanide, or
actinide, additionally, germanium (Ge), antimony (Sb) and polonium
(Po), and silicon (Si). In some embodiments, the alloy is a
metal-metal alloy. In other embodiments, the alloy is a
metal-non-metal alloy. In certain embodiments, metal-metal alloys
are prepared by utilizing a first metal precursor, a second metal
precursor, and optional further metal precursors in a fluid stock
in a process described herein described herein (e.g., evenly
dispersing the at least two metal precursors), wherein the first
and second metal precursors comprise different metals. In some
embodiments, metal-non-metal alloys are prepared by utilizing a
metal precursor and a non-metal stock (e.g., powder of the
non-metal material) in a fluid stock in a process described herein
described herein (e.g., evenly dispersing the metal precursor and
the non-metal stock in the fluid stock), wherein the first and
second metal precursors comprise different metals.
[0228] In various embodiments, metal alloys optionally comprise any
metal discussed above for metal nanofibers (as the metal alloy
nanofibers discussed are considered within the scope of metal
nanofibers for the purposes of this disclosure). In addition, for
metal-non-metal alloys, any suitable non-metal material, such as
boron, carbon, phosphorus, sulfur, selenium, or the like, may be
utilized. For example, FIG. 25 illustrates a lead selenium
metal-non-metal alloy prepared according to the disclosure provided
herein.
[0229] Provided in various embodiments herein are metal alloy
nanofibers, nanofibers comprising metal alloy, or nanofibers
substantially comprised of metal alloy. In some embodiments, the
metal alloy nanofiber comprises about 99%, about 98%, about 97%,
about 96%, about 95%, about 90%, about 80%, and the like of metal
alloy by mass. In some embodiments, the metal alloy nanofiber
comprises at least about 99%, at least about 98%, at least about
97%, at least about 96%, at least about 95%, at least about 90%, at
least about 80%, and the like of ceramic by mass (e.g., elemental
mass). In other embodiments, metal alloy nanofibers provided herein
comprise at least 50%, at least 60%, at least 70%, or at least 75%
metal alloy by mass (e.g., elemental mass). In specific
embodiments, metal alloy nanofibers provided herein comprise at
least 80% metal alloy by mass. In more specific embodiments, metal
alloy nanofibers provided herein comprise at least 90% metal alloy
by mass. In still more specific embodiments, metal alloy nanofibers
provided herein comprise at least 95% metal alloy by mass.
[0230] In some embodiments, the metal alloy nanofibers comprise low
amounts of carbon and/or oxygen as discussed herein for metal
nanofibers. In certain embodiments, wherein the metal-non metal
alloy is a metal-carbon alloy, at least 50%, at least 60%, at least
70%, or at least 75% metal and carbon by mass (e.g., elemental
mass). In specific embodiments, metal alloy nanofibers provided
herein comprise at least 80% metal and carbon by mass. In more
specific embodiments, metal alloy nanofibers provided herein
comprise at least 90% metal and carbon by mass. In still more
specific embodiments, metal alloy nanofibers provided herein
comprise at least 95% metal and carbon by mass.
[0231] Exemplary metal alloys include, but are not limited to CdSe,
CdTe, PbSe, PbTe, FeNi (perm alloy), Fe--Pt intermetallic compound,
Pt--Pb, Pt--Pd, Pt--Bi, Pd--Cu, and Pd--Hf. Methods for producing
metal alloy nanofibers are disclosed herein and optionally include
electrospinning a fluid stock comprising a mixture of the metal
precursors of the alloy and calcinating under reducing conditions.
For example, a CdSe alloy nanofiber is produced by electrospinning
a fluid stock comprising a mixture of cadmium acetates and selenium
acetates, followed by calcinating under reducing conditions.
[0232] In one aspect, in addition to metal, ceramic, or alloy
nanofibers, a nanofiber of virtually any material is produced using
the methods described herein (e.g., as long as the material is
convertible from suitable precursors distributed substantially
evenly and in a high proportion of the fluid stock). In some
embodiments, the nanofiber is a calcium phosphate (Ca--P)
nanofiber. In some embodiments, the methods of the present
disclosure produce high quality Ca--P nanofibers, optionally
wherein the nanofiber is at least 50 .mu.m long on average.
[0233] In some embodiments, the methods of the present disclosure
are combined with other methods to produce yet more embodiments.
For example, the nanofibers undergo further modifications following
their synthesis. As disclosed in U.S. patent application Ser. No.
12/439,398 for example, biologically functional additives are added
to calcium phosphate nanofibers for culturing bone and dental cells
or as implants to treat bone, dental or periodontal diseases and
defects.
[0234] In some embodiments, the nanofibers are surface-modified.
For example, enzymes are immobilized on the nanofiber surface to
create a biological catalyst. In another example, doping processes
from the semiconductor industry are employed to introduce
impurities into a pure semiconductor nanofiber (e.g., for the
purpose of modulating its electrical properties).
[0235] In one aspect, described herein is a nanofiber comprising a
segment comprising a continuous matrix of a metal, a metal oxide, a
metal alloy, a ceramic, or a combination thereof. In some
instances, a continuous matrix is conductive from one end of the
segment to the other end of the segment. In some instances, a
continuous matrix defines a single unified volume of the metal,
metal oxide, metal alloy, ceramic, or a combination thereof. In
some instances, the metal, metal oxide, metal alloy, ceramic, or a
combination thereof is in contact with metal, metal oxide, metal
alloy, ceramic, or a combination thereof all along the length of
the continuous matrix. The segment or plurality of segments
comprise any suitable proportion of the nanofiber, including about
5%, about 10%, about 20%, about 30%, about 40%, about 50%, about
60%, about 70%, about 80%, about 90%, about 95%, and the like of
the length of the nanofiber. In some embodiments, the segment or
segments comprise at most 5%, at most 10%, at most 20%, at most
30%, at most 40%, at most 50%, at most 60%, at most 70%, at most
80%, at most 90%, at most 95%, and the like of the length of the
nanofiber. In some embodiments, the segment or segments comprise at
least 5%, at least 10%, at least 20%, at least 30%, at least 40%,
at least 50%, at least 60%, at least 70%, at least 80%, at least
90%, at least 95%, and the like of the length of the nanofiber. In
specific embodiments, a continuous matrix described herein
comprises less than half of the mass of the nanofiber, but forms
the continuous matrix that runs along the length of the nanofiber.
In some instances, the continuous matrix runs along at least 50%
the length of the nanofiber (e.g., on average for populations of
nanofibers). In specific instances, the continuous matrix runs
along at least 70% the length (e.g., on average) of the
nanofiber(s). In more specific instances, the continuous matrix
runs along at least 80% the length (e.g., on average) of the
nanofiber(s). In still more specific embodiments, the continuous
matrix runs along at least 90% of the length (e.g., on average) of
the nanofiber(s). In yet more specific embodiments, the continuous
matrix runs along at least 95% of the length (e.g., on average) of
the nanofiber(s).
Composite & Hybrid nanofibers
[0236] Previous methods for producing nanofibers (e.g., the sol-gel
method) do not generally produce nanofibers of a high enough
quality to be any form other than a solid monolithic cylinder. In
some instances, by employing the methods disclosed herein, the
number and size of voids and defects in nanofibers are
substantially reduced, allowing more complex geometries such as
hollow nanofibers and composite or hybrid nanofibers made of more
than one material. In some instances, the hybrid or hollow
nanofibers are suitably long and continuous (i.e., high
quality).
[0237] In some embodiments, provided herein is a composite
nanofiber comprising a first material and a second material. In
some embodiments, at least one or both of the first and second
materials comprise a metal or metal oxide (e.g., metal oxide
ceramic).
[0238] In certain embodiments, the first material forms a
continuous matrix of the nanofiber. In specific embodiments, the
first material is a metal, a ceramic, or carbon. In more specific
embodiments, the first material is a metal or carbon and the second
material is a metal, metal oxide (e.g., metal oxide ceramic), or
ceramic. In some embodiments, the first material is a ceramic and
the second material is a metal, metal oxide, or ceramic. In
specific embodiments, the first material is a ceramic and the
second material is a metal.
[0239] In some embodiments, the first material forms a continuous
matrix and the second material forms isolated domains within the
nanofiber. In other embodiments, both the first and second
materials form continuous matrices within the nanofiber (e.g., a
layered hybrid nanofiber, such as a layered hybrid nanofiber formed
via coaxial electrospinning--a layered coaxial hybrid nanofiber).
In other embodiments, the first and second materials form different
(e.g., alternating) segments of the nanofiber (i.e., alternating
segments along the length of the nanofiber).
[0240] Described herein are methods for producing hybrid
nanofibers, methods for using hybrid nanofibers, devices comprising
hybrid nanofibers, and the hybrid nanofibers themselves. As
disclosed herein, hybrid nanofibers are useful in flexible solar
cells for example. "Hybrid" is used interchangeably with
"composite" and means that the nanofiber comprises at least two
materials. The materials are found in distinct locations on or in
the nanofiber. Such locations are arranged in any suitable
geometric matter.
[0241] One exemplary geometry is a fiber with various annular rings
or layers made of different materials. In some embodiments, each
layer is coaxial. In some embodiments, coaxial hybrid nanofibers
are produced by the methods described herein (e.g., comprising at
least two layers--one of which may form a core of the nanofiber,
the other a layer at least partially surrounding the core). In some
embodiments, the spinneret is modified to comprise a first conduit
containing a first fluid stock surrounded by a second conduit
containing a second fluid stock (FIG. 35). In some instances, the
fluid stocks are drawn or forced through the conduits. Such a
configuration produces an annular fluid jet with the second fluid
stock surrounding the first fluid stock. In some embodiments, as
the jet dries and is then calcified, the first and second fluid
stocks do not substantially mix, so are converted into different
materials in the nanofiber.
[0242] In some embodiments of a hybrid nanofiber (e.g., including a
coaxial nanofiber), various layers are any material suitable. In
some embodiments, the coaxial layers are referred to in any manner
unless the context clearly indicates otherwise. For example, for a
nanofiber consisting of two coaxial layers, the first layer may
surround the second layer or the second layer may surround the
first layer. In some embodiments, the first coaxial layer comprises
a ceramic. In some embodiments the second coaxial layer comprises a
ceramic. In some embodiments, the first coaxial layer comprises a
metal. In some embodiments the second coaxial layer comprises a
metal. In various embodiments, the hybrid nanofiber is
metal-on-metal, ceramic-on-metal, ceramic-on-ceramic, or
metal-on-ceramic. In some embodiments, the hybrid nanofiber has at
least 3 components, including any integer with all types of
materials in all types of combinations.
[0243] In various embodiments, composite nanofibers comprise metal,
metal oxide, and/or ceramic, as disclosed herein. The metals, metal
oxides, and/or ceramics used in such composite nanofibers include
any such metals, metal oxides, or ceramics described herein for
metal (e.g., single metal or alloys), metal oxide (e.g., metal
oxide ceramics), and ceramic nanofibers. In some embodiments, a
metal like Ag, Cu, Ni, Fe, Co, Pb, Au, Sn, Al, is hybridized with a
ceramic like Al.sub.2O.sub.3, ZrO.sub.2, Fe.sub.2O.sub.3, CuO, MO,
ZnO, CdO, SiO.sub.2, TiO.sub.2, V.sub.2O.sub.5, VO.sub.2,
Fe.sub.3O.sub.4, SnO, SnO.sub.2, CoO, CoO.sub.2, CO.sub.3O.sub.4,
HfO.sub.2, BaTiO.sub.3, SrTiO.sub.3, BaSrTiO.sub.3. In some
embodiments, a first co-axial layer comprises Ni or Fe. In some
embodiments, a second co-axial layer comprises Al.sub.2O.sub.3,
ZrO.sub.2, SiO.sub.2 or TiO.sub.2. In one embodiment, a first
co-axial layer comprises Ni and a second co-axial layer comprises
ZrO.sub.2. In one embodiment, a first coaxial layer comprises
Al.sub.2O.sub.3, and a second co-axial layer comprises ITO. In
another embodiment, a first coaxial layer comprises ZrO.sub.2 and a
second co-axial layer comprises ZnO.
[0244] Complex geometries other than coaxial fibers are also
described herein. For example in one arrangement, a first and a
second material are disposed along different parts of the length of
the nanofiber. In some embodiments, such a nanofiber is produced by
alternating the fluid stock between a first fluid stock comprising
a first material and a second fluid stock comprising a second
material in the electrospinning process. In such an embodiment,
upon calcination a nanofiber is produced that alternates along its
length between a first material and a second material. The first
and second materials are any suitable material, including ceramics
and metals.
[0245] In various embodiments, a composite nanofiber comprises a
metal-metal hybrid, a metal-ceramic hybrid, or the like. In some
embodiments, the nanofiber is a hybrid of both metal and ceramic.
In certain embodiments, the mass percentages of the total mass of
the metal and ceramic components of the nanofiber are added (to the
extent that either or both are present) and comprise about 99.99%,
about 99.95%, about 99.9%, about 99%, about 98%, about 97%, about
96%, about 95%, about 90%, about 80%, and the like of the
nanofiber. In other embodiments, the sum of the metal and ceramic
components of the nanofiber are at least about 99.99%, at least
about 99.95%, at least about 99.9%, at least about 99%, at least
about 98%, at least about 97%, at least about 96%, at least about
95%, at least about 90%, at least about 80%, and the like of the
nanofiber. In other embodiments, the total mass of the metal and
ceramic components (to the extent that either or both are present)
comprise at least 30%, at least 40%, at least 50%, at least 60%, at
least 70%, or the like. In some instances, these lower
metal/ceramic content composite nanofibers are present nanofibers
comprising a continuous matrix that is neither metal nor
ceramic.
[0246] FIGS. 16-21 and 31-33 illustrate metal precursor and metal
composite/hybrid nanofibers provided herein and/or as prepared
according to the processes described herein. FIG. 16 illustrates
zirconium-zinc precursor nanofibers 1601 (i.e., nanofibers
comprising zirconium precursor, zinc precursor, and polymer) having
average diameters of 600-1000 nm, and zirconia-zinc oxide composite
nanofibers 1602, having average diameters of 300-600 nm, prepared
from the precursor nanofibers 1601 after treatment at 600.degree.
C. for 2 hours in argon. FIG. 16 also illustrates the crystal x-ray
diffraction peaks for zirconia 1603 and zinc oxide 1604 for the
composite nanofibers 1602. FIG. 17 illustrates zirconium-silver
precursor nanofibers 1701 having average diameters of 700-900 nm,
and zirconia-silver composite nanofibers 1702, having average
diameters of 400-700 nm, prepared from the precursor nanofibers
1701 after treatment at 800.degree. C. for 2 hours in an
argon/hydrogen mixture. FIG. 17 also illustrates the crystal x-ray
diffraction peaks for zirconia 1703 and silver 1704 for the
composite nanofibers 1702.
[0247] FIG. 18 illustrates zirconium-nickel precursor nanofibers
1801 having average diameters of 800-1200 nm, and zirconia-nickel
composite nanofibers 1802, having average diameters of 600-800 nm,
prepared from the precursor nanofibers 1801 after treatment at
600.degree. C. for 2 hours in argon. FIG. 18 also illustrates the
crystal x-ray diffraction peaks for zirconia 1803 and nickel 1804
for the composite nanofibers 1802. FIG. 19 illustrates
zirconium-iron precursor nanofibers 1901 having average diameters
of 600-1000 nm, and zirconia-iron composite nanofibers 1902, having
average diameters of 400-700 nm, prepared from the precursor
nanofibers 1901 after treatment at 600.degree. C. for 2 hours in
argon. FIG. 19 also illustrates the crystal x-ray diffraction peaks
for zirconia 1903 and iron 1904 for the composite nanofibers 1902.
FIG. 20 further illustrates TEM images for such nanocomposites.
FIG. 21 illustrates aluminum-nickel precursor nanofibers 2101
having average diameters of 400-1100 nm, and alumina-nickel
composite nanofibers 2102, having average diameters of 150-700 nm,
prepared from the precursor nanofibers 2101 after treatment at
600.degree. C. for 2 hours in argon. FIG. 21 also illustrates the
crystal x-ray diffraction peaks for nickel 2103 (and no peaks for
the amorphous alumina) for the composite nanofibers 2102. FIG. 31
illustrates zirconium-nickel precursor nanofibers 3101 (nickel
precursor+polymer core and zirconium precursor+polymer sheath)
having average diameters of 450-700 nm, and zirconia-nickel layered
composite nanofibers 3102, having average diameters of 300-550 nm,
prepared from the precursor nanofibers 3101 after treatment at
600.degree. C. for 2 hours in argon. FIG. 31 also illustrates the
crystal x-ray diffraction peaks for zirconia and nickel 3103 for
the layered (i.e., coaxial) composite nanofibers 3102 (nickel metal
core and zirconia sheath). FIG. 32 illustrates TEM images for
coaxial/layered layered nickel/zirconia nanofibers and FIG. 33
illustrates elemental analysis of coaxial/layered layered
nickel/zirconia nanofibers. Panel A of FIG. 33 illustrates a hybrid
nanofiber comprising a zirconium oxide layer outside of a nickel
layer (core). Panel B of FIG. 33, illustrates the high content of
zirconium and oxygen relative to nickel and carbon (in a ratio of
about 18:32:4:2, respectively).
Hollow Nanofibers
[0248] The present disclosure encompasses methods for producing
hollow nanofibers, methods for using hollow nanofibers, devices
incorporating hollow nanofibers, and the hollow nanofibers
themselves. As disclosed herein, hollow nanofibers are useful in
lithium ion batteries in some instances.
[0249] In some embodiments, hollow nanofibers are produced using a
spinneret that comprises a first conduit containing a first fluid
surrounded by a second conduit containing a second fluid. In some
instances, the first fluid is any fluid that does not become an
integral part of the nanofiber (e.g., a gas). In some embodiments,
the first fluid is inert.
[0250] In some embodiments, the first fluid is a gas, optionally
air. In some instances, there are certain advantages to using a gas
as the inner annular fluid as described in the gas-assisted
electrospinning technique as disclosed in PCT Patent Application
PCT/US2011/024894 ("Electrospinning apparatus and nanofibers
produced therefrom"). In some embodiments, the gas jet accelerates
and elongates the fluid stock stream emanating from the
electrospinner, leading to thinner fibers. In some instances, the
methods disclosed herein lead to thinner nanofibers (e.g., when
using the gas-assisted method) and nanofibers that have few defects
(e.g., so are therefore high quality).
[0251] In some embodiments, the first (inert) fluid is a liquid,
optionally mineral oil for example. In embodiments where the outer
fluid stock is aqueous, the mineral oil core does not mix with the
electrospun fluid stock. In some embodiments, the mineral oil core
is removed following calcination to leave a hollow nanofiber.
[0252] In some embodiments, hollow nanofibers are produced without
an inert inner annular fluid. For example, a coaxial hybrid
nanofiber is produced, then the inner annual material is removed,
leaving a hollow nanofiber. The inner material is removed by any
suitable technique including dissolving, subliming, evaporating,
degrading, etching, or equivalents that result in a hollow
nanofiber.
[0253] The hollow core of the nanofiber has any suitable diameter.
In some embodiments, a given collection of nanofibers comprise
nanofibers that have a distribution of fibers with various
diameters of the hollow core. In some embodiments, a single
nanofiber has a hollow core diameter that varies along its length.
In some embodiments, certain fibers of a population or portions of
a fiber exceed or fall short of the average inner diameter. In some
embodiments, the diameter of the hollow core is on average about 1
nm, about 2 nm, about 3 nm, about 4 nm, about 5 nm, about 6 nm,
about 7 nm, about 8 nm, about 9 nm, about 10 nm, about 15 nm, about
20 nm, about 40 nm, about 60 nm, about 80 nm, about 100 nm, about
200 nm, about 300 nm, about 400 nm, about 500 nm, and the like. In
some embodiments, the diameter of the hollow core is on average at
most about 1 nm, at most about 2 nm, at most about 3 nm, at most
about 4 nm, at most about 5 nm, at most about 6 nm, at most about 7
nm, at most about 8 nm, at most about 9 nm, at most about 10 nm, at
most about 15 nm, at most about 20 nm, at most about 40 nm, at most
about 60 nm, at most about 80 nm, at most about 100 nm, at most
about 200 nm, at most about 300 nm, at most about 400 nm, at most
about 500 nm, and the like. In some embodiments, the diameter of
the hollow core is on average at least about 1 nm, at least about 2
nm, at least about 3 nm, at least about 4 nm, at least about 5 nm,
at least about 6 nm, at least about 7 nm, at least about 8 nm, at
least about 9 nm, at least about 10 nm, at least about 15 nm, at
most least 20 nm, at least about 40 nm, at least about 60 nm, at
least about 80 nm, at least about 100 nm, at least about 200 nm, at
least about 300 nm, at least about 400 nm, at least about 500 nm,
and the like. In some embodiments, the diameter of the hollow core
is on average between about 1 nm and 10 nm, between about 5 nm and
20 nm, between about 5 nm and 10 nm, between about 10 nm and 50 nm,
between about 20 nm and 50 nm, between about 1 nm and 50 nm,
between about 100 nm and 500 nm, and the like.
Nanofiber Properties
[0254] In one aspect, the nanofibers described herein are unique
compositions of matter, having never before been described. In one
aspect, described herein are nanofibers having certain novel
properties. In various embodiments, these nanofibers have certain
dimensions, aspect ratios, specific surface areas, porosities,
conductivities, flexibilities, and the like that are beyond what
was previously achievable. In some embodiments, the nanofibers
described herein offer improvement upon devices that comprise the
nanofibers. For example, the metal nanofibers described herein have
an electrical conductivity that is at least 70% of the conductivity
of the material when formed into a sheet in some instances. In some
embodiments, high conductivity improves the function of solar cells
based on the novel metal nanofibers.
[0255] In some embodiments, certain applications favor smaller
diameter nanofibers (e.g., which are achieved without sacrificing
quality by practicing the methods described herein). For example,
gas-assisted electrospinning techniques are utilized to create thin
nanofibers (i.e., by accelerating the jet stream of fluid stock
leaving the electrospinner). In some embodiments, the diameter of
the nanofiber changes upon calcination, optionally shrinking. In
one example, copper nanofibers were 600 to 800 nm in diameter when
electrospun and 300 to 500 nm after calcination. In some
embodiments, the loading of precursor on the polymer affects the
diameter of the nanofiber. In some embodiments, thicker nanofibers
result from higher precursor loadings (e.g., because there is more
precursor material converted into the nanofiber). Methods for
measuring the diameter of a nanofiber include, but are not limited
to microscopy, optionally transmission electron microscopy ("TEM")
or scanning electron microscopy ("SEM").
[0256] In various embodiments, provided herein are nanofibers or
processes for producing nanofibers having any suitable diameter. In
some embodiments, a given collection of nanofibers comprise
nanofibers that have a distribution of fibers of various diameters.
In some embodiments, a single nanofiber has a diameter that varies
along its length. In some embodiments, certain fibers of a
population or portions of a fiber exceed or fall short of the
average diameter. In some embodiments, the nanofiber has on average
a diameter of about 20 nm, about 30 nm, about 40 nm, about 50 nm,
about 60 nm, about 70 nm, about 80 nm, about 90 nm, about 100 nm,
about 130 nm, about 150 nm, about 200 nm, about 250 nm, about 300
nm, about 400 nm, about 500 nm, about 600 nm, about 700 nm, about
800 nm, about 900 nm, about 1,000 nm, about 1,500 nm, about 2,000
nm and the like. In some embodiments, the nanofiber has on average
a diameter of at most 20 nm, at most 30 nm, at most 40 nm, at most
50 nm, at most 60 nm, at most 70 nm, at most 80 nm, at most 90 nm,
at most 100 nm, at most 130 nm, at most 150 nm, at most 200 nm, at
most 250 nm, at most 300 nm, at most 400 nm, at most 500 nm, at
most 600 nm, at most 700 nm, at most 800 nm, at most 900 nm, at
most 1,000 nm, at most 1,500 nm, at most 2,000 nm and the like. In
some embodiments, the nanofiber has on average a diameter of at
least 20 nm, at least 30 nm, at least 40 nm, at least 50 nm, at
least 60 nm, at least 70 nm, at least 80 nm, at least 90 nm, at
least 100 nm, at least 130 nm, at least 150 nm, at least 200 nm, at
least 250 nm, at least 300 nm, at least 400 nm, at least 500 nm, at
least 600 nm, at least 700 nm, at least 800 nm, at least 900 nm, at
least 1,000 nm, at least 1,500 nm, at least 2,000 nm and the like.
In yet other embodiments, the nanofiber has on average a diameter
between about 50 nm and about 300 nm, between about 50 nm and about
150 nm, between about 100 nm and about 400 nm, between about 100 nm
and about 200 nm, between about 500 nm and about 800 nm, between
about 60 nm and about 900 nm, and the like. In specific
embodiments, nanofibers (e.g., metal, metal oxide, ceramic, and/or
composite nanofibers described herein) have a (e.g., average)
diameter of less than 1500 nm. In more specific embodiments,
nanofibers (e.g., metal, metal oxide, ceramic, and/or composite
nanofibers) described herein have a (e.g., average) diameter of 100
nm to 1000 nm. In some embodiments, nanofibers described herein
(e.g., those comprising metal/metal oxide/ceramic) have a (e.g.,
average) diameter of 500 nm or less. In some embodiments,
nanofibers described herein (e.g., those comprising metal/metal
oxide/ceramic) have a (e.g., average) diameter of 400 nm or less.
In some embodiments, nanofibers described herein (e.g., those
comprising metal/metal oxide/ceramic) have a (e.g., average)
diameter of 200 nm to 500 nm. In other specific embodiments,
precursor nanofibers described herein have a (e.g., average)
diameter of less than 2000 nm. In more specific embodiments,
precursor nanofibers described herein have a (e.g., average)
diameter of 300 nm to 1500 nm.
[0257] In some embodiments, the nanofiber is long. In some
instances, the methods of the present disclosure produce long
nanofibers (e.g., because the high loading and uniform distribution
of precursor creates nanofibers that are highly "continuous" or
"coherent", meaning that they have few defects). In some
embodiments, such high quality nanofibers are statistically more
likely to be long because the probability is reduced that there is
a defect along any particular length that is severe enough to
define an end of the nanofiber. Methods for measuring the length of
a nanofiber include, but are not limited to microscopy, optionally
transmission electron microscopy ("TEM") or scanning electron
microscopy ("SEM").
[0258] The nanofibers have any suitable length. In some instances,
a given collection of nanofibers comprise nanofibers that have a
distribution of fibers of various lengths. In some embodiments,
certain fibers of a population exceed or fall short of the average
length. In some embodiments, the nanofiber has an average length of
about 20 .mu.m, about 50 .mu.m, about 100 .mu.m, about 500 .mu.m,
about 1,000 .mu.m, about 5,000 .mu.m, about 10,000 .mu.m, about
50,000 .mu.m, about 100,000 .mu.m, about 500,000 .mu.m, and the
like. In some embodiments, the nanofiber has an average length of
at least about 20 .mu.m, at least about 50 .mu.m, at least about
100 .mu.m, at least about 500 .mu.m, at least about 1,000 .mu.m, at
least about 5,000 .mu.m, at least about 10,000 .mu.m, at least
about 50,000 .mu.m, at least about 100,000 .mu.m, at least about
500,000 .mu.m, and the like.
[0259] "Aspect ratio" is the length of a nanofiber divided by its
diameter. In some instances, aspect ratio is a useful metric for
quantifying the coherence of a nanofiber, with higher aspect ratios
indicating that a nanofiber or population of nanofibers have few
voids or defects. In some embodiments, aspect ratio refers to a
single nanofiber. In some embodiments, aspect ratio refers to a
plurality of nanofibers and is reported as a single average value
(i.e., the aspect ratio being the average length of the nanofibers
of a sample divided by their average diameter). In some instances,
diameters and/or lengths are measured by microscopy. The nanofibers
have any suitable aspect ratio. In some embodiments, the nanofiber
has an aspect ratio of about 5, about 10, about 10.sup.2, about
10.sup.3, about 10.sup.4, about 10.sup.5, about 10.sup.6, about
10.sup.7, about 10.sup.8, about 10.sup.9, about 10.sup.10, about
10.sup.11, about 10.sup.12, and the like. In some embodiments the
nanofiber has an aspect ratio of at least about 5, at least 10, at
least 10.sup.2, at least 10.sup.3, at least 10.sup.4, at least
10.sup.5, at least 10.sup.6, at least 10', at least 10.sup.8, at
least 10.sup.9, at least 10.sup.10, at least 10.sup.11, at least
10.sup.12, and the like. In some embodiments, the nanofiber is of
substantially infinite length and has an aspect ratio of
substantially infinity. In specific embodiments, the aspect ratio
(e.g., average aspect ratio) of nanofibers provided herein is at
least 100. In more specific embodiments, the aspect ratio (e.g.,
average aspect ratio) of nanofibers provided herein is at least
1,000 (e.g., at least 5,000). In still more specific embodiments,
the aspect ratio (e.g., average aspect ratio) of nanofibers
provided herein is at least 10,000.
[0260] In some embodiments, the nanofibers have a high surface
area. In some embodiments, the nanofiber is used as a catalyst
where reactions take place on the surface of the nanofiber. In
these catalyst embodiments, a high surface area reduces the size of
the process equipment and/or reduces the amount of expensive
material required in the catalyst.
[0261] The "specific surface area" is the surface area per mass or
volume one of a fiber (or an average of a plurality of fibers). In
various instances, the specific surface area is calculated based on
a single nanofiber, or based on a collection of nanofibers and
reported as a single average value. Techniques for measuring mass
are known to those skilled in the art. In some instances, the
surface area is calculated by measuring the diameter and length of
nanofiber in the sample and applying the equation for the surface
area of a cylinder (i.e., 2 times pi times half of the diameter of
the nanofiber times the sum of the length of the nanofiber and half
of the diameter of the nanofiber). In some instances, the surface
area is measured by physical or chemical methods, for example by
the Brunauer-Emmett, and Teller (BET) method where the difference
between physisorption and desorption of inert gas is utilized. In
some embodiments, the surface area is measured by titrating certain
chemical groups on the nanofiber to estimate the number of groups
on the surface, which is related to the surface area by a
previously determined titration curve. Those skilled in the art of
chemistry will be familiar with methods of titration.
[0262] The nanofiber has any suitable specific surface area. In
some embodiments, the specific surface area is about 0.1 m.sup.2/g,
about 0.5 m.sup.2/g, about 1.0 m.sup.2/g, about 5 m.sup.2/g, about
10 m.sup.2/g, about 40 m.sup.2/g, about 60 m.sup.2/g, about 80
m.sup.2/g, about 100 m.sup.2/g, about 200 m.sup.2/g, about 400
m.sup.2/g, about 600 m.sup.2/g, about 800 m.sup.2/g, about 1,000
m.sup.2/g, about 1,500 m.sup.2/g, about 2,000 m.sup.2/g, and the
like. In some embodiments, the specific surface area is at least
0.1 m.sup.2/g, at least 0.5 m.sup.2/g, at least 1.0 m.sup.2/g, at
least 5 m.sup.2/g, at least 10 m.sup.2/g, at least 40 m.sup.2/g, at
least 60 m.sup.2/g, at least 80 m.sup.2/g, at least 100 m.sup.2/g,
at least 200 m.sup.2/g, at least 400 m.sup.2/g, at least 600
m.sup.2/g, at least 800 m.sup.2/g, at least 1,000 m.sup.2/g, at
least 1,500 m.sup.2/g, at least 2,000 m.sup.2/g, and the like. In
some embodiments, the specific surface area is between about 0.1
m.sup.2/g and 1 m.sup.2/g, between about 1 m.sup.2/g and 1,000
m.sup.2/g, between about 10 m.sup.2/g and 100 m.sup.2/g, between
about 600 m.sup.2/g and 2,000 m.sup.2/g, between about 10 m.sup.2/g
and 1,000 m.sup.2/g, between about 100 m.sup.2/g and 600 m.sup.2/g,
between about 300 m.sup.2/g and 500 m.sup.2/g, and the like.
[0263] In some instances, methods disclosed herein (e.g., including
using a high loading of uniformly distributed precursor) reduce the
number and size of pores. Porosity is also called "void fraction"
and is a measure of the void spaces in a material. In some
embodiments, porosity is a fraction of the volume of voids over the
total volume and is reported as a percentage between 0% and 100%.
In various embodiments, the porosity depends on many factors
including loading and distribution of precursor in the fluid stock,
calcination conditions, and the like.
[0264] Methods for measuring or estimating porosity include
microscopy. Methods also include first measuring the surface area
of a sample of nanofibers by any direct or indirect method, then
comparing the measured surface area with the surface area of an
idealized cylinder having the average length and diameter of the
nanofibers in the sample. In some embodiments, the difference
between the measured and expected surface area is converted to a
volume, then to a volume fraction by assuming that the pores are in
the shape of spheres or cylinders having an average diameter. In
some embodiments, the porosity is measured by immersing the
nanofibers in a fluid that penetrates the pores. In such an
embodiment, the porosity is estimated by comparing the total volume
of nanofiber plus fluid with the volume that would be obtained from
immersing a collection of idealized non-porous cylinders having the
diameter and length of the nanofibers. The void volume is the
difference between these volumes, which is converted to porosity by
dividing the void volume by the volume of the idealized
cylinders.
[0265] The nanofibers have any suitable porosity. In some
embodiments, the porosity is about 1%, about 2%, about 4%, about
6%, about 8%, about 10%, about 15%, about 20%, about 25%, about
30%, about 40%, about 50%, about 60%, about 70% and the like. In
some embodiments, the porosity is at most 1%, at most 2%, at most
4%, at most 6%, at most 8%, at most 10%, at most 15%, at most 20%,
at most 25%, at most 30%, at most 40%, at most 50%, at most 60%, at
most 70% and the like. In some embodiments, the porosity is at
least 1%, at least 2%, at least 4%, at least 6%, at least 8%, at
least 10%, at least 15%, at least 20%, at least 25%, at least 30%,
at least 40%, at least 50%, at least 60%, at least 70% and the
like. In some embodiments, the porosity is between about 1% and
10%, between about 10% and 50%, between about 20% and 30%, between
about 30% and 70%, between about 1% and 50%, between about 5% and
20%, and the like.
[0266] In certain embodiments, nanofibers provided herein have
improved performance over other nano-materials. In some instances,
Young's modulus, fracture toughness, ultimate strength, electrical
conductivity, thermal conductivity, flexibility, and/or other
characteristics of the nanofibers described herein (and/or their
composite materials) are improved over other nanostructures of the
same material and/or over the bulk/sheet form of the same material.
Table 1 illustrates the physical properties of certain nanofibers
provided herein and the physical properties of bulk materials
having similar structure. In some embodiments, provided herein are
ceramic or metal oxide nanofibers (or nanofibers having a
continuous matrix of ceramic and/or metal oxide) having an average
Young's Modulus at least the level (or at least 90% the level) of a
ceramic set forth in Table 1 (particularly rows 1 or 2 for
amorphous ceramics, row 3 from crystalline ceramics, or row 4 or 5
for metal oxides). In some embodiments, provided herein are ceramic
or metal oxide nanofibers (or nanofibers having a continuous matrix
of ceramic and/or metal oxide) having an average Fracture Toughness
at least the level (or at least 90% the level) as set forth in
Table 1 (particularly rows 1 or 2 for amorphous ceramics, row 3
from crystalline ceramics, or row 4 or 5 for metal oxides). In
certain embodiments, provided herein are ceramic or metal oxide
nanofibers (or nanofibers having a continuous matrix of ceramic
and/or metal oxide) having an average Ultimate Strength at least
the level (or at least 90% the level) as set forth in Table 1
(particularly rows 1 or 2 for amorphous ceramics, row 3 from
crystalline ceramics, or row 4 or 5 for metal oxides). In some
embodiments, provided herein are metal nanofibers (or nanofibers
having a continuous matrix of metal) having an average Young's
Modulus at least the level (or at least 90% the level) of a ceramic
set forth in Table 1 (particularly rows 6, 7, or 8). In some
embodiments, provided herein are metal nanofibers (or nanofibers
having a continuous matrix of metal) having an average Fracture
Toughness at least the level (or at least 90% the level) as set
forth in Table 1 (particularly rows 6, 7, or 8). In certain
embodiments, provided herein are metal nanofibers (or nanofibers
having a continuous matrix of metal) having an average Ultimate
Strength at least the level (or at least 90% the level) as set
forth in Table 1 (particularly rows 6, 7, or 8). In some
embodiments, provided herein are metal nanofibers (or nanofibers
having a continuous matrix of metal) having an average electrical
conductivity of at least the level (or at least 90% the level) as
set forth in Table 1 (particularly rows 6, 7, or 8).
TABLE-US-00001 TABLE 1 Youngs Modulus Fracture Ultimate Strength
Electrical Conductivity (GPa) Toughness (MPa) (log(S/m)) Material
nanofiber bulk (MPa m.sup.1/2) nanofiber bulk nanofiber bulk
SiO.sub.2 79 80 0.71 41 33 -- (amorphous) Al.sub.2O.sub.3 81 0.99
77 -- (amorphous) ZrO.sub.2 818 210 2.15 2612 1900 -- --
(crystalline) ZnO 137 1.4 109 2.9 Fe.sub.2O.sub.3 118 1.32 144 3.3
Cu 608 117 4.12 191 70 6.6 7.4 Ni 407 2.81 123 5.1 Fe 299 1.47 218
4.6 ZrO.sub.2/ 718 1.88 1011 -- Ni nanocrystals (~5:1)
[0267] In some embodiments, nanofibers described herein have
improved Young's modulus over similar materials in other
nanostructure or bulk forms. In some instances, provided herein are
nanofibers having a mean or median nanofiber Young's
modulus-to-diameter ratio of at least 0.1 GPa/nm. In certain
instances, provided herein are nanofibers having a mean or median
nanofiber Young's modulus-to-diameter ratio of at least 0.13
GPa/nm. In specific instances, provided herein are nanofibers
having a mean or median nanofiber Young's modulus-to-diameter ratio
of at least 0.15 GPa/nm. In more specific instances, provided
herein are nanofibers having a mean or median nanofiber Young's
modulus-to-diameter ratio of at least 0.18 GPa/nm. In still more
specific instances, provided herein are nanofibers having a mean or
median nanofiber Young's modulus-to-diameter ratio of at least 0.2
GPa/nm. In yet more specific instances, provided herein are
nanofibers having a mean or median nanofiber Young's
modulus-to-diameter ratio of at least 0.25 GPa/nm. In specific
instances, provided herein are nanofibers having a mean or median
nanofiber Young's modulus-to-diameter ratio of at least 0.3 GPa/nm.
In some instances, provided herein are nanofibers having a mean or
median nanofiber Young's modulus-to-diameter ratio of at least 0.05
GPa/nm or at least 0.5 GPa/nm.
[0268] In some embodiments, provided herein are amorphous ceramic
nanofibers (e.g., pure amorphous ceramic nanofibers, as described
herein, or nanofibers comprising a amorphous ceramic continuous
matrix) comprising an average Young's modulus-to-diameter ratio of
at least 0.15 GPa/nm. In specific embodiments, provided herein are
amorphous ceramic nanofibers comprising an average Young's
modulus-to-diameter ratio of at least 0.2 GPa/nm. In still more
specific embodiments, provided herein are amorphous ceramic
nanofibers comprising an average Young's modulus-to-diameter ratio
of at least 0.3 GPa/nm. In yet more specific embodiments, provided
herein are amorphous ceramic nanofibers comprising an average
Young's modulus-to-diameter ratio of at least 0.35 GPa/nm. In some
embodiments, provided herein are amorphous ceramic nanofibers
comprising an average ultimate strength-to-diameter ratio of at
least 0.05 MPa/nm. In specific embodiments, provided herein are
amorphous ceramic nanofibers comprising an average ultimate
strength-to-diameter ratio of at least 0.075 MPa/nm. In yet more
specific embodiments, provided herein are amorphous ceramic
nanofibers comprising an average ultimate strength-to-diameter
ratio of at least 0.1 MPa/nm. In still more specific embodiments,
provided herein are amorphous ceramic nanofibers comprising an
average ultimate strength-to-diameter ratio of at least 0.15
MPa/nm. In yet more specific embodiments, provided herein are
amorphous ceramic nanofibers comprising an average ultimate
strength-to-diameter ratio of at least 0.2 MPa/nm. In some
embodiments, provided herein are amorphous ceramic nanofibers
comprising an average ultimate strength-to-diameter ratio of at
least 0.075 MPa/nm and an average Young's modulus-to-diameter ratio
of at least 0.15 GPa/nm. In more specific embodiments, provided
herein are amorphous ceramic nanofibers comprising an average
ultimate strength-to-diameter ratio of at least 0.15 MPa/nm and an
average Young's modulus-to-diameter ratio of at least 0.3 GPa/nm.
In some embodiments, provided herein are amorphous ceramic
nanofibers having a fracture toughness of at least 0.5
MPam.sup.1/2. In specific embodiments, provided herein are
amorphous ceramic nanofibers having a fracture toughness of at
least 0.6 MPam.sup.1/2. In more specific embodiments, provided
herein are amorphous ceramic nanofibers having a fracture toughness
of at least 0.7 MPam.sup.1/2.
[0269] In some embodiments, provided herein are crystalline ceramic
nanofibers (e.g., pure crystalline ceramic nanofibers, as described
herein, or nanofibers comprising a crystalline ceramic continuous
matrix) comprising an average Young's modulus-to-diameter ratio of
at least 1 GPa/nm. In specific embodiments, provided herein are
crystalline ceramic nanofibers comprising an average Young's
modulus-to-diameter ratio of at least 1.5 GPa/nm. In still more
specific embodiments, provided herein are crystalline ceramic
nanofibers comprising an average Young's modulus-to-diameter ratio
of at least 2 GPa/nm. In yet more specific embodiments, provided
herein are crystalline ceramic nanofibers comprising an average
Young's modulus-to-diameter ratio of at least 3 GPa/nm. In more
specific embodiments, provided herein are crystalline ceramic
nanofibers comprising an average Young's modulus-to-diameter ratio
of at least 4 GPa/nm. In some embodiments, provided herein are
crystalline ceramic nanofibers comprising an average ultimate
strength-to-diameter ratio of at least 3 MPa/nm. In specific
embodiments, provided herein are crystalline ceramic nanofibers
comprising an average ultimate strength-to-diameter ratio of at
least 5 MPa/nm. In yet more specific embodiments, provided herein
are crystalline ceramic nanofibers comprising an average ultimate
strength-to-diameter ratio of at least 7.5 MPa/nm. In still more
specific embodiments, provided herein are crystalline ceramic
nanofibers comprising an average ultimate strength-to-diameter
ratio of at least 10 MPa/nm. In yet more specific embodiments,
provided herein are crystalline ceramic nanofibers comprising an
average ultimate strength-to-diameter ratio of at least 12.5
MPa/nm. In some embodiments, provided herein are crystalline
ceramic nanofibers comprising an average ultimate
strength-to-diameter ratio of at least 5 MPa/nm and an average
Young's modulus-to-diameter ratio of at least 1.5 GPa/nm. In more
specific embodiments, provided herein are crystalline ceramic
nanofibers comprising an average ultimate strength-to-diameter
ratio of at least 12.5 MPa/nm and an average Young's
modulus-to-diameter ratio of at least 4 GPa/nm. In some
embodiments, provided herein are crystalline ceramic nanofibers
having an average fracture toughness of at least 1.5 MPam.sup.1/2.
In specific embodiments, provided herein are crystalline ceramic
nanofibers having an average fracture toughness of at least 1.8
MPam.sup.1/2. In more specific embodiments, provided herein are
crystalline ceramic nanofibers having an average fracture toughness
of at least 2.1 MPam.sup.1/2.
[0270] In some embodiments, provided herein are metal nanofibers
(e.g., pure metal nanofibers, as described herein, or nanofibers
comprising a metal continuous matrix) comprising an average Young's
modulus-to-diameter ratio of at least 0.8 GPa/nm. In specific
embodiments, provided herein are metal nanofibers comprising an
average Young's modulus-to-diameter ratio of at least 1.1 GPa/nm.
In still more specific embodiments, provided herein are metal
nanofibers comprising an average Young's modulus-to-diameter ratio
of at least 1.5 GPa/nm. In yet more specific embodiments, provided
herein are metal nanofibers comprising an average Young's
modulus-to-diameter ratio of at least 2 GPa/nm. In more specific
embodiments, provided herein are metal nanofibers comprising an
average Young's modulus-to-diameter ratio of at least 2.9 GPa/nm.
In some embodiments, provided herein are metal nanofibers
comprising an average ultimate strength-to-diameter ratio of at
least 0.2 MPa/nm. In specific embodiments, provided herein are
metal nanofibers comprising an average ultimate
strength-to-diameter ratio of at least 0.35 MPa/nm. In yet more
specific embodiments, provided herein are metal nanofibers
comprising an average ultimate strength-to-diameter ratio of at
least 0.5 MPa/nm. In still more specific embodiments, provided
herein are metal nanofibers comprising an average ultimate
strength-to-diameter ratio of at least 0.7 MPa/nm. In yet more
specific embodiments, provided herein are metal nanofibers
comprising an average ultimate strength-to-diameter ratio of at
least 0.9 MPa/nm. In some embodiments, provided herein are metal
nanofibers comprising an average ultimate strength-to-diameter
ratio of at least 0.35 MPa/nm and an average Young's
modulus-to-diameter ratio of at least 1.1 GPa/nm. In more specific
embodiments, provided herein are metal nanofibers comprising an
average ultimate strength-to-diameter ratio of at least 0.9 MPa/nm
and an average Young's modulus-to-diameter ratio of at least 2.9
GPa/nm. In some embodiments, provided herein are metal nanofibers
having an average fracture toughness of at least 3 MPam.sup.1/2. In
specific embodiments, provided herein are metal nanofibers having
an average fracture toughness of at least 3.5 MPam.sup.1/2. In more
specific embodiments, provided herein are metal nanofibers having a
average fracture toughness of at least 4.1 MPam.sup.1/2. In some
embodiments, the average electrical conductivity of a metal
nanofiber provided herein has a log(S/m) to log(S/m) ratio with an
identical bulk material of at least 0.75 (i.e., log of the
electrical conductivity along the length of the metal nanofiber
divided by log of the electrical conductivity of the same metal, in
bulk). In specific embodiments, the average electrical conductivity
of a metal nanofiber provided herein has a log(S/m) to log(S/m)
ratio with an identical bulk material of at least 0.85. In more
specific embodiments, the average electrical conductivity of a
metal nanofiber provided herein has a log(S/m) to log(S/m) ratio
with an identical bulk material of at least 0.9. In still more
specific embodiments, the average electrical conductivity of a
metal nanofiber provided herein has a log(S/m) to log(S/m) ratio
with an identical bulk material of at least 0.95.
[0271] In some embodiments, applications of the nanofibers
described herein benefit from nanofibers having a high
conductivity. In some instances, a high electrical conductivity is
desirable in energy generation applications that involve moving
electrons through the nanofiber (e.g., as an electrode of a
battery). In some embodiments, nanofibers that are long and
continuous with a reduced number or size of defects have a higher
conductivity.
[0272] In various embodiments, conductivity means either "thermally
conductivity", "electrically conductivity", or both thermally and
electrically conductivity unless context clearly dictates
otherwise. Electrical conductivity is a measure of a material's
ability to conduct electric current. Electrical conductivity is
measured in units of Siemens per length (e.g., S/cm). The
reciprocal of conductivity is resistivity. Electrical resistivity
is a measure of how strongly a material opposes the flow of
electric current and is reported in units of ohm meter (em). In
some instances, thermal conductivity is reported in units of watts
per meter Kelvin (W/m/K). Thermal resistivity is the reciprocal
thereof. Inspection of the units indicates whether the value is
electrical or thermal conductivity.
[0273] In one aspect, the nanofiber has a conductivity (e.g.,
electrical or thermal) which is compared to a thin sheet of the
material from which the nanofiber is made. For example, a copper
nanofiber is compared with a thin sheet of copper. The nanofibers
have any suitable conductivity as a percentage of the conductivity
of the material is formed into a sheet. In some embodiments, the
conductivity is variable over different portions of a collection of
nanofibers, or along different directions. In various embodiments,
conductivity is reported as either an average value, or a value
specific to a certain condition or direction of measurement (i.e.,
for anisotropic materials).
[0274] In some embodiments, the nanofiber has a conductivity of
about 5%, about 10%, about 20%, about 30%, about 40%, about 50%,
about 60%, about 70%, about 80%, about 90%, about 95%, or about
100% when compared with the conductivity of the material when
formed into a sheet. In some embodiments, the nanofiber has a
conductivity of at least about 5%, at least about 10%, at least
about 20%, at least about 30%, at least about 40%, at least about
50%, at least about 60%, at least about 70%, at least about 80%, at
least about 90%, at least about 95%, or at least about 100% when
compared with the conductivity of the material when formed into a
sheet. In some embodiments, the nanofiber has a conductivity of at
most about 5%, at most about 10%, at most about 20%, at most about
30%, at most about 40%, at most about 50%, at most about 60%, at
most about 70%, at most about 80%, at most about 90%, at most about
95%, or at most about 100% when compared with the conductivity of
the material when formed into a sheet. In some embodiments, the
nanofiber has a conductivity of between about 5% and 10%, between
about 10% and 20%, between about 20% and 30%, between about 30% and
40%, between about 40% and 50%, between about 50% and 60%, between
about 60% and 70%, between about 70% and 80%, between about 80% and
90%, between about 90% and 95%, between about 95% and 100%, when
compared with the conductivity of the material when formed into a
sheet.
[0275] In some instances, conductivity is reported without
reference to the conductivity of the material when formed into a
sheet. For example in some embodiments, electrical conductivity is
reported on an absolute, rather than relative basis. Electrical
conductivity is measured by any suitable method known to those
skilled in the art. For example in some embodiments, conductivity
is measured by first measuring the resistance and calculating the
reciprocal. In one instance, one hooks up a sample of nanofibers to
be tested to a voltage source and measures the current going
through the sample and the voltage across the sample. In some
instances, the resistance is calculated from Ohm's law (i.e., R=E/I
where R is resistance in ohms, E is voltage in volts and I is
current in amperes). Once one has resistance, one can calculate
resistivity. Resistivity is a factor, which when multiplied by the
length of the sample and divided by its cross-sectional area,
yields the resistance. Conductivity is the reciprocal of the
resistivity.
[0276] The nanofibers have any suitable electrical conductivity. In
various embodiments, electrical conductivity is measured as an
average value, at a specific condition, or along a specific
direction of the nanofiber sample. In some embodiments, the
conductivity is about 1 S/cm, about 10 S/cm, about 100 S/cm, about
10.sup.3 S/cm, about 10.sup.4 S/cm, about 10.sup.5 S/cm, about
10.sup.6 S/cm, about 10.sup.7 S/cm, about 10.sup.8 S/cm, and the
like. In some embodiments, the conductivity is at least 1 S/cm, at
least 10 S/cm, at least 100 S/cm, at least 10.sup.3 S/cm, at least
10.sup.4 S/cm, at least 10.sup.5 S/cm, at least 10.sup.6 S/cm, at
least 10.sup.7 S/cm, at least 10.sup.8 S/cm, and the like. In some
embodiments, the conductivity is at most 1 S/cm, at most 10 S/cm,
at most 100 S/cm, at most 10.sup.3 S/cm, at most 10.sup.4 S/cm, at
most 10.sup.5 S/cm, at most 10.sup.6 S/cm, at most 10.sup.7 S/cm,
at most 10.sup.8 S/cm, and the like. In some embodiments, the
conductivity is between about 1 S/cm and 10 S/cm, between about 10
S/cm and 100 S/cm, between about 100 S/cm and 1,000 S/cm, between
about 1,000 S/cm and 10.sup.4 S/cm, between about 10.sup.4 S/cm and
10.sup.5 S/cm, between about 10.sup.5 S/cm and 10.sup.6 S/cm,
between about 10.sup.6 S/cm and 10.sup.7 S/cm, between about
10.sup.7 S/cm and 10.sup.8 S/cm, between about 10.sup.5 S/cm and
10.sup.8 S/cm, and the like.
[0277] In some embodiments, the nanofibers or collections of
nanofibers of the present disclosure are flexible. In some
instances, flexible nanofibers are advantageous in applications
such as in the manufacture of flexible solar panels. In some
instances, flexibility is quantified by the Young's modulus, which
is the slope of the initial linear portion of a stress-strain
curve. The Young's modulus has units of pressure, such as mega
Pascals (MPa). In some embodiments, flexibility is different along
different directions of the material, so may be reported with
respect to a certain direction, or is reported as an average
value.
[0278] In one aspect, the flexibility is at least partially
determined by the calcination temperature. In one example, when the
calcination temperature is about 200.degree. C. the Young's modulus
is at least 100 MPa. In some instances, lower calcination
temperatures lead to a significantly higher fraction of amorphous
metal or ceramic in the nanofiber, which results in higher
flexibility.
[0279] The nanofibers have any suitable flexibility. In some
embodiments, the nanofiber has a Young's modulus of about 10 MPa,
about 20 MPa, about 40 MPa, about 60 MPa, about 80 MPa, about 100
MPa, about 150 MPa, about 200 MPa, about 250 MPa, about 300 MPa,
about 400 MPa, about 1,000 MPa, and the like. In some embodiments,
the nanofiber has a Young's modulus of at least about 10 MPa, at
least about 20 MPa, at least about 40 MPa, at least about 60 MPa,
at least about 80 MPa, at least about 100 MPa, at least about 150
MPa, at least about 200 MPa, at least about 250 MPa, at least about
300 MPa, at least about 400 MPa, at least about 1,000 MPa, and the
like.
Nanofiber Mats
[0280] In some embodiments, the nanofibers described herein are
collected or formed into any suitable structure (e.g., suitable for
the desired application). Structures include, but are not limited
to spheres, cones, cylinders, slabs, helixes, polygons, and the
like. For simplicity of terminology, all possible shapes or
assemblage of nanofibers are herein referred to as a "mat". In
various embodiments, nanofiber mats comprise nanofibers of a single
type, or nanofibers of at least two types.
[0281] In some embodiments, coherent nanofibers lead to a mat
having desirable properties (e.g., a less brittle nanofiber mat).
In some instances, these desirable properties emerge from the
properties of the component nanofibers and/or depend on the method
in which the nanofibers are formed into the mat. In some
embodiments, the present disclosure includes the nanofiber mats. In
one aspect, described herein are nanofiber mats formed by the
nanofibers of the present disclosure. Also described herein are
nanofiber mats prepared by any of the methods, or preparable by any
of the methods in the present disclosure. In one aspect, described
herein are methods for preparing nanofiber mats, optionally using
an electrospinning process.
[0282] In some embodiments, nanofibers are collected in a given
geometry as they are produced (e.g., by moving the collection plate
relative to the spinnerets, i.e., 3-D printing). In various
embodiments, nanofibers are formed into a given geometry after
collection (optionally before calcination), or formed into a given
geometry after calcination. In some instances, the nanofiber mat
comprises nanofibers arranged in a controlled manner (e.g., on a
mesh with a perpendicular lattice). In some embodiments, the
nanofibers are arranged randomly. In various embodiments, the mats
are patterned in any level of detail including different fibers of
different types, laid in different directions, in contact with
various other nanofibers or insulated from various other
nanofibers, and the like. In some embodiments, the nanofibers are
cross-linked and/or surface modified.
[0283] In some nanofiber mats, the nanofiber surface proves a high
surface area for mass transfer of a chemical product. These
nanofibers are particularly applicable as catalysts for example. In
some embodiments, the nanofiber surface proves a high surface area
for mass transfer of a protons or electrons in the nanofiber mat.
These nanofibers are particularly applicable as electrodes for
example.
[0284] In some instances, nanofibers provided herein are assembled
into a nanofiber mat. In some instances, use of nanofiber mats
provide for the improvement of certain nanofiber performance
characteristics. For example, FIG. 39 shows a graphic comparing the
effect of fiber alignment conditions on electrical conductivity in
the axial and perpendicular direction of a Ni nanofiber mat.
Properties of Nanofiber Mats
[0285] In some instances, the nanofiber mat has substantially the
same properties as the nanofibers from which it is comprised. For
example, a similar porosity, similar specific surface area, similar
specific conductivity, and the like. In some instances, the
nanofiber mat has different properties from the nanofibers from
which it is comprised. For example, a different porosity, different
specific surface area, different conductivity, and the like. In
various embodiments, the property of the mat is either greater than
or less than the property of an individual nanofiber.
[0286] In some embodiments, the nanofiber mat is "isotropic" or has
isotropic properties (e.g., meaning that the nanofiber mat has the
same or substantially similar properties in all orientations and
along all directions of the material). In some embodiments, the mat
is "anisotropic" (e.g., meaning that it has different properties in
various orientations or along different directions of the
material). In some embodiments, anisotropic properties are created
by controlling the orientation of the nanofibers in the mat. For
example, in one embodiment where nanofiber direction was uniformly
controlled, there was an approximately 100 fold difference in
electric conductivity of copper nanofibers between the axial
direction (direction of the nanofiber) and the perpendicular
direction.
[0287] In embodiments where the mat is anisotropic, a given
property differs in a second orientation or direction compared to a
first orientation or direction by about 5%, about 10%, about 15%,
about 20%, about 30%, about 40%, about 50%, about 60%, about 80%,
about 100%, about 150%, about 200%, about 300%, about 400%, about
500%, and the like. In some embodiments, a given property is about
10 times, about 20 times, about 50 times, about 100 times, about
200 times, about 500 times, about 1,000 times, about 10,000 times,
and the like higher in a second direction or orientation than in a
first direction or orientation.
[0288] In some embodiments, a given property differs in a second
orientation or direction compared to a first orientation or
direction by at least about 5%, at least about 10%, at least about
15%, at least about 20%, at least about 30%, at least about 40%, at
least about 50%, at least about 60%, at least about 80%, at least
about 100%, at least about 150%, at least about 200%, at least
about 300%, at least about 400%, at least about 500%, and the like.
In some embodiments, a given property is at least about 10 times,
at least about 20 times, at least about 50 times, at least about
100 times, at least about 200 times, at least about 500 times, at
least about 1,000 times, at least about 10,000 times, and the like
higher in a second direction or orientation than in a first
direction or orientation.
[0289] In some embodiments, a given property differs in a second
orientation or direction compared to a first orientation or
direction by at most about 5%, at most about 10%, at most about
15%, at most about 20%, at most about 30%, at most about 40%, at
most about 50%, at most about 60%, at most about 80%, at most about
100%, at most about 150%, at most about 200%, at most about 300%,
at most about 400%, at most about 500%, and the like. In some
embodiments, a given property is at most about 10 times, at most
about 20 times, at most about 50 times, at most about 100 times, at
most about 200 times, at most about 500 times, at most about 1,000
times, at most about 10,000 times, and the like higher in a second
direction or orientation than in a first direction or
orientation.
[0290] In some embodiments, the mat has a conductivity in a first
direction and a conductivity in a second direction, wherein the
conductivity in the first direction is at least one hundred times
higher than in the second direction. In some embodiments, the mat
has a conductivity of at least 1.0 S/cm in either the first or
second direction.
[0291] In some instances, the porosity of the nanofiber mat is a
consideration, for example in filtration applications. For example,
in order to remove particles of a certain diameter, it is desirable
to have a mat with pores smaller than the diameter of the smallest
particle to be removed in some instances.
[0292] In some embodiments, the porosity of the nanofiber mat is
greater than the porosity of the nanofibers that comprise the mat.
In some embodiments, the porosity of the mat is the combination of
the spaces between the nanofiber strands and the pores within the
nanofibers themselves. In some instances, microscopy is used to
estimate porosity. In some instances, the porosity of a nanofiber
mat having a first volume defined by its external surface is
measured by submersing the nanofiber mat in a fluid having a second
volume. The volume of the fluid plus submersed nanofiber mat
defines a third volume. A fourth volume is obtained by subtracting
the second volume from the third volume. The porosity is one minus
the ratio of the fourth volume to the first volume. In some
embodiments, porosity is expressed as a percentage.
[0293] The nanofiber mat has any suitable porosity. In some
embodiments, the porosity is about 1%, about 2%, about 4%, about
6%, about 8%, about 10%, about 15%, about 20%, about 25%, about
30%, about 40%, about 50%, about 60%, about 70% and the like. In
some embodiments, the porosity is at most 1%, at most 2%, at most
4%, at most 6%, at most 8%, at most 10%, at most 15%, at most 20%,
at most 25%, at most 30%, at most 40%, at most 50%, at most 60%, at
most 70% and the like. In some embodiments, the porosity is at
least 1%, at least 2%, at least 4%, at least 6%, at least 8%, at
least 10%, at least 15%, at least 20%, at least 25%, at least 30%,
at least 40%, at least 50%, at least 60%, at least 70% and the
like. In some embodiments, the porosity is between about 1% and
10%, between about 10% and 50%, between about 20% and 30%, between
about 30% and 70%, between about 1% and 50%, between about 5% and
20%, and the like.
[0294] In some instances, porosity has units of length. The porous
length is the distance between a point on a nanofiber strand and
the nearest point on another nanofiber strand. In some instances,
objects having a dimension longer than this porous length will not
generally be able to pass through the mat. In some instances, the
porous length is measured by bombarding the nanofiber mat with
particles of a plurality of diameters until the particles of a
certain size pass through the nanofiber mat, indicating that the
nanofiber mat has a porous length approximately equal to the
diameter of said particles.
[0295] The pores of the nanofiber mat have any suitable size. In
some embodiments, the pores are about 0.1 microns, about 0.2
microns, about 0.5 microns, about 0.7 microns, about 1 microns,
about 2 microns, about 4 microns, about 6 microns, about 8 microns,
about 10 microns, about 15 microns, about 20 microns, about 30
microns, about 40 microns, about 50 microns, about 70 microns,
about 100 microns, about 200 microns, and the like on their longest
dimension. In some embodiments, the pores are at most about 0.1
microns, at most about 0.2 microns, at most about 0.5 microns, at
most about 0.7 microns, at most about 1 microns, at most about 2
microns, at most about 4 microns, at most about 6 microns, at most
about 8 microns, at most about 10 microns, at most about 15
microns, at most about 20 microns, at most about 30 microns, at
most about 40 microns, at most about 50 microns, at most about 70
microns, at most about 100 microns, at most about 200 microns, and
the like on their longest dimension. In other embodiments, the
pores are at least about 0.1 microns, at least about 0.2 microns,
at least about 0.5 microns, at least about 0.7 microns, at least
about 1 microns, at least about 2 microns, at least about 4
microns, at least about 6 microns, at least about 8 microns, at
least about 10 microns, at least about 15 microns, at least about
20 microns, at least about 30 microns, at least about 40 microns,
at least about 50 microns, at least about 70 microns, at least
about 100 microns, at least about 200 microns, and the like on
their longest dimension. In some embodiments, the pores are between
about 0.5 microns and 50 microns, between about 1 microns and 10
microns, between about 10 microns and 50 microns, between about 0.1
microns and 5 microns, between about 2 microns and 10 microns,
between about 40 microns and 100 microns, and the like on their
longest dimension.
[0296] In some instances, the density of the nanofiber mat is
another characteristic to consider in certain applications. In some
instances, the concentration of the polymer in the fluid stock has
an impact on the density of the mat (e.g., potentially with
decreased amounts of polymer leading to a denser mat, e.g., because
fewer voids are left when the polymer is removed in calcination).
In one example, the density of the mat was at least about 1
g/m.sup.3 where the polymer was less than about 30% in the fluid
stock.
[0297] The nanofiber mat has any suitable density. In some
embodiments, the mat has a density of about 0.01 g/cm.sup.3, about
0.05 g/cm.sup.3, about 0.1 g/cm.sup.3, about 0.2 g/cm.sup.3, about
0.4 glcm.sup.3, about 0.8 g/cm.sup.3, about 1 g/cm.sup.3, about 5
g/cm.sup.3, about 10 g/cm.sup.3, and the like. In some embodiments,
the mat has a density of at least about 0.01 g/cm.sup.3, at least
about 0.05 g/cm.sup.3, at least about 0.1 g/cm.sup.3, at least
about 0.2 g/cm.sup.3, at least about 0.4 g/cm.sup.3, at least about
0.8 g/cm.sup.3, at least about 1 g/cm.sup.3, at least about 5
g/cm.sup.3, at least about 10 g/cm.sup.3, and the like. In some
embodiments, the mat has a density of at most about 0.01
g/cm.sup.3, at most about 0.05 g/cm.sup.3, at most about 0.1
g/cm.sup.3, at most about 0.2 g/cm.sup.3, at most about 0.4
g/cm.sup.3, at most about 0.8 g/cm.sup.3, at most about 1
g/cm.sup.3, at most about 5 g/cm.sup.3, at most about 10
g/cm.sup.3, and the like. In some embodiments, the mat has a
density of between about 0.01 g/cm.sup.3 and 0.05 g/cm.sup.3,
between about 0.05 g/cm.sup.3 and 0.3 g/cm.sup.3, between about 0.1
g/cm.sup.3 and 1 g/cm.sup.3, between about 1 g/cm.sup.3 and 5
g/cm.sup.3, and the like.
[0298] The mat has any suitable number of strands per area or
volume. In some instances, microscopy is used to determine the
number of strands per area or volume. In some embodiments, the mat
comprises about 5 strands, about 10 strands, about 50 strands,
about 100 strands, about 150 strands, about 250 strands, about 500
strands, about 1,000 strands, about 5,000 strands, about 50,000
strands, and the like per square millimeter or per cubic
millimeter. In some embodiments, the mat comprises at least about 5
strands, at least about 10 strands, at least about 50 strands,
about 100 strands, at least about 150 strands, at least about 250
strands, at least about 500 strands, at least about 1,000 strands,
at least about 5,000 strands, at least about 50,000 strands, and
the like per square millimeter or per cubic millimeter. In some
embodiments, the mat comprises between about 5 strands to 50
strands, between about 50 strands to 500 strands, between about 500
strands to 5,000 strands, between about 5,000 strands to 50,000
strands, and the like per square millimeter or per cubic
millimeter.
[0299] In some instances, the sizes of the crystal domains in the
nanofiber have an effect on properties of the nanofiber or
nanofiber mat (e.g., including magnetic strength and electrical
conductivity). In some instances, calcination conditions have an
effect on crystallization domains. In some embodiments, one may
control the properties of the nanofiber or nanofiber mat by
controlling the calcination conditions. In one example, FIG. 38
shows that by tuning calcination conditions with Ni nanofibers, a
5-fold difference in magnetic strength was obtained and a 10,000
fold difference in electric conductivity was obtained. Described
herein are nanofibers or nanofiber mats having crystal domains of a
certain size. The present disclosure also encompasses nanofibers or
nanofiber mats with tunable properties and methods for tuning the
properties of nanofiber or nanofiber mats (e.g., including magnetic
or conductivity properties).
[0300] In some embodiments, there are a plurality of crystal
domains in the nanofiber. In some embodiments, the domains are
metal oxide domains. In various embodiments, these domains have
various sizes, for example about 1 nm, about 5 nm, about 10 nm,
about 15 nm, about 20 nm, about 25 nm, about 30 nm, about 40 nm,
about 50 nm, about 70 nm, about 90 nm, and the like. In some
embodiments, the domains are at least about 1 nm, at least about 5
nm, at least about 10 nm, at least about 15 nm, at least about 20
nm, at least about 25 nm, at least about 30 nm, at least about 40
nm, at least about 50 nm, at least about 70 nm, at least about 90
nm, and the like in size. In some embodiments, the domains are at
most about 1 nm, at most about 5 nm, at most about 10 nm, at most
about 15 nm, at most about 20 nm, at most about 25 nm, at most
about 30 nm, at most about 40 nm, at most about 50 nm, at most
about 70 nm, at most about 90 nm, and the like in size. In some
embodiments, the domains have a size between about 1 nm and 100 nm,
between about 20 nm and 30 nm, between about 1 nm and 20 nm,
between about 30 nm and 90 nm, between about 40 nm and 70 nm,
between about 15 nm and 40 nm, and the like.
[0301] In one aspect, the nanofiber and/or nanofiber mat is
magnetic. The coercivity (also called the coercive field or
coercive force) of a ferromagnetic material is the intensity of the
applied magnetic field required to reduce the magnetization of that
material to zero after the magnetization of the sample has been
driven to saturation. Coercivity is usually measured in oersted
(Oe) or ampere/meter units.
[0302] In some embodiments, the nanofiber mat has any suitable
magnetic coercivity. In some embodiments, the nanofiber mat has a
magnetic coercivity of about 10 Oe, about 20 Oe, about 40 Oe, about
60 Oe, about 80 Oe, about 100 Oe, about 125 Oe, about 150 Oe, about
175 Oe, about 200 Oe, about 250 Oe, about 300 Oe, about 350 Oe,
about 400 Oe, about 500 Oe, about 1,000 Oe, and the like. In some
embodiments, the nanofiber mat has a magnetic coercivity of at
least about 10 Oe, at least about 20 Oe, at least about 40 Oe, at
least about 60 Oe, at least about 80 Oe, at least about 100 Oe, at
least about 125 Oe, at least about 150 Oe, at least about 175 Oe,
at least about 200 Oe, at least about 250 Oe, at least about 300
Oe, at least about 350 Oe, at least about 400 Oe, at least about
500 Oe, at least about 1,000 Oe, and the like. In some embodiments,
the nanofiber mat has a magnetic coercivity of at most about 10 Oe,
at most about 20 Oe, at most about 40 Oe, at most about 60 Oe, at
most about 80 Oe, at most about 100 Oe, at most about 125 Oe, at
most about 150 Oe, at most about 175 Oe, at most about 200 Oe, at
most about 250 Oe, at most about 300 Oe, at most about 350 Oe, at
most about 400 Oe, at most about 500 Oe, at most about 1,000 Oe,
and the like. In some embodiments, the nanofiber mat has a magnetic
coercivity of between about 50 Oe and 2000e, between about 100 Oe
and 300 Oe, between about 200 Oe and 500 Oe, between about 300 Oe
and 1,000 Oe, between about 10 Oe and 100 Oe, between about 175 Oe
and 300 Oe, between about 200 Oe and 250 Oe, and the like.
[0303] In one aspect, the nanofiber and/or nanofiber mat is
paramagnetic or superparamagnetic. Paramagnetism is a form of
magnetism that occurs in the presence of an externally applied
magnetic field. Superparamagnetism is a form of magnetism which
appears in small ferromagnetic or ferrimagnetic nanoparticles or
nanofibers. In some instances (e.g., for sufficiently small
nanoparticles or nanofibers), magnetization randomly flips
direction under the influence of temperature. The time between two
flips is called the Neel relaxation time. In the absence of
external magnetic field, when the time used to measure the
magnetization of the nanoparticles is much longer than the Neel
relaxation time, their magnetization appears to be on average zero.
That is, they are said to be in the superparamagnetic state. In
this state, an external magnetic field is able to magnetize the
nanoparticles or nanofibers, similarly to a paramagnet.
System
[0304] In some embodiments, a number of components of a system
interact to produce nanofibers. Without limitation, these include
an electrospinning apparatus and a module for collecting the
electrospun fluid stock or nanofiber. These two components are
related by a voltage difference such that the thin jet of fluid
stock emanating from the electrospinner is attracted to and
deposits on the collection module. In some embodiments, the
electrospinning component of the system is a gas-assisted
electrospinner. The gas used to accelerate the jet of fluid stock
is optionally air.
[0305] In some embodiments, the system also includes a fluid stock.
Among other things, the fluid stock interacts with the
electrospinner to produce a nanofiber. In some embodiments, the
fluid stock has an elongational viscosity that allows for a jet of
fluid stock to erupt from a charged droplet. In some embodiments,
the fluid stock is a system of polymer and precursor that interact
with each other to at least in part determine the spinnability of
the fluid stock and the properties of the nanofiber.
[0306] In some embodiments, the system also includes an apparatus
for calcinating the nanofiber (e.g., a heater or a gas chamber). In
some instances, the gas is part of the system, wherein the gas is
optionally air, hydrogen, nitrogen, an inert gas, and the like.
Electrochemical Devices
[0307] Electrochemical devices include fuel cells, batteries,
capacitors and ultra-capacitors, among others. In some instances,
solar cells are electrochemical devices. In some instances, other
electrochemical devices do not fit within the categories listed
herein. In various embodiments, electrochemical devices have a wide
range of energy densities and power densities that are summarized
graphically on a Ragone chart (FIG. 40). Energy density is reported
in units of watt-hours per kilogram (Wh/kg) or equivalents and is a
measure of the amount of useful energy stored in a given size
device (by mass or volume). Power density is reported in units of
watts per kilogram (W/kg) or equivalents and is a measure of how
quickly energy can be utilized. In some instances, fuel cells have
a high energy density, but a low power density. In some instances,
capacitors have a high power density but a low energy density. In
some instances, batteries and ultracapacitors have energy densities
and power densities between capacitors and fuel cells.
[0308] In one aspect, described herein are uses of nanofibers in
electrochemical devices. For example, they are used as electrodes
in fuel cells or batteries (e.g., where they may have beneficial
properties such as a high conductivity and surface area). In some
embodiments, they are utilized as the dielectric layer in an
ultracapacitor. In various aspects, the present disclosure includes
an electrochemical device that includes the nanofibers described
herein, includes an electrochemical device that includes a
nanofiber produced by the methods described herein, and includes an
electrochemical device that includes a nanofiber produced by the
system described herein. In some aspects, the disclosure also
includes methods for making and methods for using electrochemical
devices that comprise nanofibers.
[0309] In some embodiments, devices are built that comprise the
nanofibers described herein. In some embodiments, such a device is
created by substituting a component of the device with nanofibers
(e.g., thus improving the function of the device), but
substantially preserving the overall architecture and design of the
device. In some embodiments, the architecture and overall design of
the device comprising nanofibers is markedly different than a fuel
cell, battery, ultracapacitor and the like.
[0310] In some instances, it is desirable to have or make an
electrochemical device with both high energy density and high power
density, for example to energize an electric vehicle that has both
a long driving range (i.e., energy density) and can be charged and
accelerate quickly (i.e., high power density). The electrochemical
device has any suitable energy and power density. In some
embodiments where the power density is at least about 100 W/kg, the
energy density is at least about 10 Wh/kg, at least about 50 Wh/kg,
at least about 100 Wh/kg, at least about 500 Wh/kg, at least about
1,000 Wh/kg, at least about 5,000 Wh/kg, and the like. In some
embodiments where the power density is at least about 500 W/kg, the
energy density is at least about 10 Wh/kg, at least about 50 Wh/kg,
at least about 100 Wh/kg, at least about 500 Wh/kg, at least about
1,000 Wh/kg, at least about 5,000 Wh/kg, and the like. In some
embodiments where the power density is at least about 1,000 W/kg,
the energy density is at least about 10 Wh/kg, at least about 50
Wh/kg, at least about 100 Wh/kg, at least about 500 Wh/kg, at least
about 1,000 Wh/kg, at least about 5,000 Wh/kg, and the like. In
some embodiments where the power density is at least about 5,000
W/kg, the energy density is at least about 10 Wh/kg, at least about
50 Wh/kg, at least about 100 Wh/kg, at least about 500 Wh/kg, at
least about 1,000 Wh/kg, at least about 5,000 Wh/kg, and the like.
In some embodiments where the power density is at least about
10,000 W/kg, the energy density is at least about 10 Wh/kg, at
least about 50 Wh/kg, at least about 100 Wh/kg, at least about 500
Wh/kg, at least about 1,000 Wh/kg, at least about 5,000 Wh/kg, and
the like.
Fuel Cells
[0311] A fuel cell is an electrochemical cell that converts
chemical energy into electrical energy. In some instances,
electricity is generated from the reaction between a fuel supply
and an oxidizing agent. In some embodiments, the reactants flow
into the cell, and the reaction products flow out of it, while the
electrolyte remains within it. In some embodiments, fuel cells are
different from electrochemical cell batteries in that they consume
a reactant from an external source (i.e., which is
replenished).
[0312] In some embodiments, fuel cells are made up of three
segments which are sandwiched together: the anode, the electrolyte,
and the cathode. In some embodiments, two chemical reactions occur
at the interfaces of the three different segments. In some
embodiments, the net result of the two reactions is that fuel is
consumed, water or carbon dioxide is created, and an electric
current is created (e.g., which can be used to power electrical
devices, normally referred to as the load). Many combinations of
fuels and oxidants are possible. In some embodiments, a hydrogen
fuel cell uses hydrogen as its fuel and oxygen (e.g., from air) as
its oxidant. Other possible fuels include hydrocarbons and
alcohols. Other possible oxidants include chlorine and chlorine
dioxide.
[0313] In some embodiments, at the anode a catalyst oxidizes the
fuel, (e.g., hydrogen), turning the fuel into a positively charged
ion and a negatively charged electron. In some embodiments, the
electrolyte is a substance specifically designed so ions can pass
through it, but the electrons do not. In some instances, the freed
electrons travel through a wire creating the electric current. In
some instances, the ions travel through the electrolyte to the
cathode. In some embodiments, once reaching the cathode, the ions
are reunited with the electrons and the two react with a third
chemical, (e.g., oxygen), to create water or carbon dioxide.
[0314] In some embodiments, a fuel cell has higher energy
conversion efficiency than other power sources (e.g., since it
converts chemical energy directly into electricity). In some
embodiments, fuel cells produce no pollution (e.g., when hydrogen
is used as the fuel) or less pollution (e.g., when hydrocarbon is
used as the fuel) compared to combustion. In some embodiments, fuel
cells operate quietly, reducing noise pollution. In some
embodiments, a fuel cell operates continuously and generates
electricity as long as the fuel is supplied. In some instances,
fuel cells are used in applications including portable electronic
devices, automobiles, and stationary power generation.
[0315] In some proton exchange membrane fuel cells, the catalyst
for hydrogen oxidation at the anode is carbon supported platinum.
Despite its popular use, the Pt/C anode system exhibits certain
drawbacks in some instances. First, the use of carbon generally
leads to the corrosion of the electrode in some embodiments.
Secondly, the platinum is an expensive catalyst. In some instances,
the fuel cells described herein comprise electrodes based on
nanofibers (e.g., avoiding the corrosion by carbon and reduce the
expensive Pt loading). In one embodiment, the nanofibers comprise
intermetallic Fe--Pt.
[0316] In one aspect, described herein is the use of nanofibers in
fuel cells. For example, they are used as electrodes, optionally
anodes or cathodes. In various aspects, described herein is a fuel
cell that comprises a nanofiber described herein, a fuel cell that
comprises a nanofiber produced by the methods described herein, and
includes a fuel cell that comprises a nanofiber produced by the
system described herein. In one aspect, described herein are
methods for making and methods for using fuel cells that comprise
nanofibers.
[0317] In various embodiments, the nanofiber comprises any suitable
material including, but not limited to iron (Fe), platinum (Pt), or
any mixture thereof. In some embodiments, the nanofiber is a pure
metal nanofiber or a metal alloy nanofiber, including any hybrid or
hollow geometry. In some embodiments, the atoms have a certain
arrangement (e.g., including a face-centered tetragonal structure).
In various embodiments, the ratio of Fe to Pt atoms in the
nanofiber of the fuel cell is about 1 Fe to 5 Pt, or about 4 Fe to
5 Pt for example. In some embodiments, the Fe and Pt atoms are
substantially evenly distributed amongst each other (i.e., the
nanofiber does not comprise aggregates of Pt or Fe). In some
embodiments, the creation of the face-centered tetragonal structure
of Fe--Pt is pursued to enhance oxygen reduction and durability
under the minimized Pt loading. In some instances, the optional
face-centered tetragonal structure also provides connectivity of
the Pt.
[0318] In some instances, a Pt/C fuel cell mixes Pt particles with
C and forms an electrode by vapor deposition of the mixture. In
certain embodiments, the nanofibers and electrodes described herein
significantly reduce the cost of the fuel cell (e.g., by using less
platinum). In some embodiments, a gas-assisted electrospinning
procedure is a cheaper and faster process than vapor
deposition.
[0319] In some embodiments, the fuel cell comprises an anode and
the anode comprises nanofibers. In some embodiments, a reduced
amount of platinum is preferred (e.g., because of cost). The anode
has any suitable amount of platinum (including no platinum). In
some embodiments, the anode has by mass percentage about 5% Pt,
about 10% Pt, about 15% Pt, about 20% Pt, about 25% Pt, about 30%
Pt, about 40% Pt, about 50% Pt, about 70% Pt, and the like. In some
embodiments, the anode has by mass percentage at most about 5% Pt,
at most about 10% Pt, at most about 15% Pt, at most about 20% Pt,
at most about 25% Pt, at most about 30% Pt, at most about 40% Pt,
at most about 50% Pt, at most about 70% Pt, and the like. In some
embodiments, the fuel cell has at least 10 fold less or at least 30
fold less Pt than a traditional Pt/C fuel cell. In some
embodiments, the amount of corrosion of the cathode is reduced
compared with a traditional Pt/C fuel cell. In certain embodiments,
the nanofibers described herein reduce or substantially eliminate
corrosion in the fuel cell. In some embodiments, reduced corrosion
(e.g., upon start-up or shut-down), improves the performance of the
fuel cell. In one aspect, the fuel cells described herein consist
of substantially no carbon. In one aspect, the fuel cells described
herein consist of substantially no carbon in the anode.
[0320] In some embodiments, the fuel cells described herein have a
high current density. The current density is any suitable value. In
some embodiments, the current density is about -0.01 mA/cm.sup.2,
about -0.02 mA/cm.sup.2, about -0.04 mA/cm.sup.2, about -0.06
mA/cm.sup.2, about -0.08 mA/cm.sup.2, about -0.1 mA/cm.sup.2, about
-0.3 mA/cm.sup.2, and the like. In some embodiments, the current
density is at least about -0.01 mA/cm.sup.2, at least about -0.02
mA/cm.sup.2, at least about -0.04 mA/cm.sup.2, at least about -0.06
mA/cm.sup.2, at least about -0.08 mA/cm.sup.2, at least about -0.1
mA/cm.sup.2, at least about -0.3 mA/cm.sup.2, and the like. In some
embodiments, the current density is about 4 times higher than a
traditional Pt/C fuel cell.
[0321] In some embodiments, the fuel cell has increased reaction
stability. In some instances, reaction stability is reported as the
number of CV cycles. Cyclic voltammetry or CV is a type of
potentiodynmic electrochemical measurement. In some cyclic
voltammetry experiments, the working electrode potential is ramped
linearly versus time (e.g., like linear sweep voltammetry). In some
instances, cyclic voltammetry takes the experiment a step further
than linear sweep voltammetry (which ends when it reaches a set
potential). When cyclic voltammetry reaches a set potential, the
working electrode's potential ramp is inverted. In some
embodiments, this inversion happens multiple times during a single
experiment. In some embodiments, the current at the working
electrode is plotted versus the applied voltage to give the cyclic
voltammogram trace. In some instances, cyclic voltammetry is used
to study the electrochemical properties of an analyte in solution.
In some embodiments, the fuel cells described herein have about
1.5.times. more, about 2.times. more, about 3.times. more, about
4.times. more, about 5.times. more, about 10.times. more, and the
like CV cycles than a traditional Pt/C fuel cell.
[0322] In one aspect, the fuel cell is significantly thinner than a
traditional Pt/C fuel cell. In some instances, reduced thickness
allows packing of more fuel cells into a given volume, increasing
overall performance and/or reducing cost. The fuel cells have any
suitable thickness. In some embodiments, the fuel cell has a
thickness of about 0.2 mm, about 0.5 mm, about 0.7 mm, about 1 mm,
about 1.5 mm, about 2 mm, about 5 mm, and the like when measured
along its shortest dimension. In some embodiments, the fuel cell
has a thickness of at most about 0.2 mm, at most about 0.5 mm, at
most about 0.7 mm, at most about 1 mm, at most about 1.5 mm, at
most about 2 mm, at most about 5 mm, and the like when measured
along its shortest dimension.
Batteries
[0323] In some instances, a battery is composed of electrochemical
cells that are connected in series and/or in parallel to provide
the required voltage and capacity. In some instances, each cell
consists of a positive and a negative electrode (both sources of
chemical reactions) separated by an electrolyte solution, which
enables ion transfer between the two electrodes. Once these
electrodes are connected externally, chemical reactions proceed in
tandem at both electrodes (i.e., thereby liberating electrons and
enabling the current to be used). In some instances, the amount of
electrical energy (typically expressed per unit of weight, e.g.,
Wh/kg or mWh/g) that a battery is able to deliver is a function of
the cell potential (V) and capacity (Ah/kg), which is linked
directly to the chemistry of the system.
[0324] In one aspect, described herein are batteries comprising
nanofibers. For example, the nanofibers are used in electrodes,
optionally anodes or cathodes. In one aspect, described herein is a
battery that includes a nanofiber as described herein, includes a
battery that includes a nanofiber produced by the methods described
herein, and includes a battery that includes a nanofiber produced
by the system described herein. In some aspects, the described
herein are methods for making and methods for using batteries that
include nanofibers.
[0325] The present disclosure encompasses all types of batteries.
In some embodiments, the battery is a rechargeable lithium battery.
In various embodiments, the nanofiber, the anode, and the cathode
are any suitable material. In embodiments of rechargeable lithium
batteries for example, silicon or germanium are used as anode
material (e.g., because these materials have a low discharge
potential and high theoretical charge capacity (about 4200 mAh/g,
and 1,600 mAh/g respectively) compared to that of graphitic carbon
(373 mAh/g)). In one embodiment, the nanofiber is a Si or Ge
nanofiber. In some embodiments, the anode includes Si or Ge
nanofibers.
[0326] In some instances, silicon anodes have limited applications
because silicon's volume changes upon insertion and extraction of
lithium, which results in pulverization and capacity fading. In
some instances, hollow nanofibers can accommodate volume changes
without pulverization. In some embodiments, the nanofibers
described herein are hollow. In some embodiments, the batteries
described herein comprise a hollow Si or Ge (or combination Si/Ge)
nanofiber.
[0327] In some embodiments, hollow Si and/or Ge nanofibers are
produced via water-based, multi-axial electrospinning. In various
embodiments, the nanofibers comprise pure SiO.sub.2, and their
hybrids with V.sub.2O.sub.5, ZrO.sub.2, TiO.sub.2, Fe, Ni, and
carbon with Fe.sub.3O.sub.4. In some embodiments, pure ceramic
nanofibers such as SiO.sub.2, Al.sub.2O.sub.3 and ZrO.sub.2, etc.
are produced via electrospinning of aqueous polymer solution
containing their precursors, followed by thermal treatment.
[0328] Hollow Si or Ge nanofibers (e.g., for lithium-ion battery
anodes) are produced in any suitable manner. In one embodiment,
mineral oil and aqueous polymer solution with Si or Ge precursor
are coaxially electrospun as core and sheath layer, respectively,
followed by the removal of mineral core to create a hollow
structure. In one embodiment, gas-assisted coaxial electrospinning
is employed (e.g., where an air stream is used as core) to create a
hollow structure during the spinning (e.g., and to stretch the
sheath layer jet of precursor solution for higher throughput).
[0329] Any suitable method of reduction is employed (e.g.,
following electrospinning of hollow Si or Ge precursor nanofibers).
In some embodiments, thermal treatment and/or chemical reduction
are applied to obtain pure hollow Si or Ge nanofibers. In some
instances, the degree of volume expansion upon insertion and
extraction of lithium in Li-ion battery applications is
evaluated.
[0330] The nanofibers described herein have any suitable amount of
volume expansion. In some embodiments, the volume expansion is
about 100%, about 200%, about 300%, about 400%, about 600%, about
800%, and the like. In some embodiments, the volume expansion is at
most about 100%, at most about 200%, at most about 300%, at most
about 400%, at most about 600%, at most about 800%, and the
like.
[0331] The batteries described herein have any suitable recharging
efficiency. In some embodiments, the recharging efficiency is about
500 mAh/g, about 800 mAh/g, about 1,200 mAh/g, about 1,600 mAh/g,
about 2,000 mAh/g, about 3,000 mAh/g, about 5,000 mAh/g, about
10,000 mAh/g, and the like. In some embodiments, the recharging
efficiency is at least about 500 mAh/g, at least about 800 mAh/g,
at least about 1,200 mAh/g, at least about 1,600 mAh/g, at least
about 2,000 mAh/g, at least about 3,000 mAh/g, at least about 5,000
mAh/g, at least about 10,000 mAh/g, and the like.
Ultracapacitors
[0332] In a conventional capacitor, energy is generally stored by
the removal of charge carriers, typically electrons, from one metal
plate and depositing them on another. In some instances, this
charge separation creates a potential between the two plates, which
is harnessed in an external circuit. In some instances, the total
energy stored increases with both the amount of charge stored and
the potential between the plates. In some instances, the amount of
charge stored per unit voltage is a function of the size, the
distance, and the material properties of the plates and the
material in between the plates (the dielectric), while the
potential between the plates is limited by breakdown of the
dielectric. In some instances, the dielectric controls the
capacitor's voltage. In some instances, changing the dielectric
material leads to higher energy density for a given size of
capacitor. In one aspect, described herein is the use of nanofibers
in capacitors. In various aspects, the present disclosure includes
a capacitor that comprises the nanofibers described herein,
includes a capacitor that includes a nanofiber produced by the
methods described herein, and includes a capacitor that includes a
nanofiber produced by the system described herein. In some aspects,
the disclosure also includes methods for making and methods for
using capacitors that include nanofibers.
[0333] An ultracapacitor, also known as an electric double-layer
capacitor (EDLC), a supercapacitor, supercondenser,
pseudocapacitor, or electrochemical double layer capacitor, is an
electrochemical capacitor with relatively high energy density. In
some instances, the energy density is on the order of hundreds of
times greater compared to conventional electrolytic capacitors. In
some instances, ultra-capacitors have a higher power density in
comparison with batteries or fuel cells.
[0334] In some instances, ultra-capacitors do not have a
conventional dielectric. In some instances, ultra-capacitors use
"plates" that are two layers of a substrate (optionally the same
substrate), rather than two separate plates separated by an
intervening substance. In some instances, this "electrical double
layer" results in the separation of charge despite the thin
physical separation of the layers (e.g., on the order of
nanometers). In some instances, the lack of a bulky layer of
dielectric in an ultra-capacitor permits the packing of plates with
much larger surface area into a given size, resulting in high
capacitances compared with a capacitor.
[0335] In various embodiments, any of the components of an
ultracapacitor comprise nanofibers (for example, porous
carbon/BaTiO.sub.3/separator). In some embodiments, the nanofibers
are produced from a water-based, gas-assisted electrospinning
process. In some embodiments, dielectric double layer comprises
nanofibers. In one aspect, described herein are ultracapacitors
comprising nanofibers. In various aspects, the present disclosure
includes an ultracapacitor that includes the nanofibers described
herein, includes an ultracapacitor that includes a nanofiber
produced by the methods described herein, and includes an
ultracapacitor that includes a nanofiber produced by the system
described herein. In some embodiments, described herein are methods
for making and methods for using ultracapacitors that comprise
nanofibers.
[0336] In some embodiments, the ultracapacitor comprises porous
carbon electrodes with a dielectric layer. In some embodiments, the
porous carbon electrodes are formed of nanofibers. In some
embodiments, nanofibers are disposed on the carbon electrodes. In
various embodiments, the nanofibers comprise any material with a
suitable dielectric constant. Non-limiting examples are
StTiO.sub.3, BaTiO.sub.3, SrBaTiO.sub.3, mixtures thereof, and
combinations thereof. In various embodiments, the nanofibers are of
any suitable geometry including hybrid or hollow nanofibers.
[0337] In some embodiments, described herein are processes for
producing nanofibers suitable for use in an ultracapacitor. In one
aspect, the process includes electrospinning a fluid stock, wherein
the fluid stock comprises precursor molecules bound to a polymer.
In some embodiments, the precursor molecules comprise Ba, St, Ti,
or mixtures thereof. In some embodiments, the process includes
thermally treating the spun nanofibers.
[0338] In some embodiments, the ultracapacitor comprises a thin
layer of dielectric nanofibers at the interface between the
electrolyte and the electrode (e.g., activated carbon electrode).
In some instances, this nanofiber layer results in an increased
capacitance. Capacitance density is reported in units of farads per
cubic centimeter (F/cm.sup.3) or equivalents. In some embodiments,
the ultra-capacitors described herein have a capacitance density of
about 10 F/cm.sup.3, about 20 F/cm.sup.3, about 50 F/cm.sup.3,
about 100 F/cm.sup.3, about 200 F/cm.sup.3, about 500 F/cm.sup.3,
about 1,000 F/cm.sup.3, and the like. In some embodiments, the
ultracapacitor have a capacitance density of at least about 10
F/cm.sup.3, at least about 20 F/cm.sup.3, at least about 50
F/cm.sup.3, at least about 100 F/cm.sup.3, at least about 200
F/cm.sup.3, at least about 500 F/cm.sup.3, at least about 1,000
F/cm.sup.3, and the like.
[0339] FIG. 45 shows a cross-sectional view of an electrolytic
double layer ultracapacitor comprising an electrolyte 4501, a
separator 4502, and an activated carbon electrode 4503.
[0340] FIG. 46 shows a cross-sectional view of barium titanate
nanofibers B laid on the activated carbon A of an ultracapacitor
(with electrolyte C).
Solar Cells
[0341] In some instances, a solar cell (also called photovoltaic
cell or photoelectric cell) is a solid state electrical device that
converts the energy of light directly into electricity by the
photovoltaic effect. In some instances, assemblies of cells are
used to make modules (e.g., solar panels), which are used to
capture energy from sunlight.
[0342] Photovoltaics is a field of technology related to the use of
photovoltaic cells to producing electricity from light (though it
is often used specifically to refer to the generation of
electricity from sunlight). In some instances, photovoltaic devices
are based on the concept of charge separation at an interface of
two materials of different conduction mechanism. In some instances,
photovoltaic devices are solid-state junction devices, usually made
of silicon, (e.g., and profiting from the experience and material
availability resulting from the semiconductor industry), however
other designs and materials can be utilized.
[0343] In various embodiments, any of the components of a solar
cell (e.g., thin film solar cell) comprise nanofibers. Exemplary
components include an anode, an n-layer, an active layer, a p-layer
and a cathode. In some embodiments, the nanofibers are produced by
the water-based, gas-assisted electrospinning process described
herein. In some embodiments, the n-layer, active layer and p-layer
comprise nanofibers. In one aspect, the present disclosure includes
uses of nanofibers in solar cells. The present disclosure includes
solar cells that include a nanofiber of the invention, includes
solar cells that include a nanofiber produced by the methods of the
invention, and includes thin film solar cells that include a
nanofiber produced by the system of the invention. The disclosure
also includes methods for making and methods for using solar cells
that include nanofibers.
[0344] In one embodiment, the cathode comprises nanofibers (e.g.,
aluminum). In various embodiments, any suitable material is used as
the cathode including pure metal nanofibers such as gold (Au),
silver (Ag), nickel (Ni), copper (Co), and/or calcium (Ca).
[0345] In some instances, the n-layer provides for transfer of
electrons. In some embodiments, the n-layer comprises ZnO
nanofibers. Any suitable bandgap material is used as the n-layer
including nanofibers of any suitable pure metal oxides such as
TiO.sub.2.
[0346] In one embodiment, the photoactive layer comprises PbSe
nanofibers (e.g., where the PbSe crystals are nanoscale in size).
Any suitable bandgap material is used as the photoactive layer
including nanofibers of any suitable hybrid materials such as CdTe,
CdS, PbS, and/or PbTe.
[0347] In some instances, the p-layer provides the transfer of
holes. In some embodiments, the p-layer comprises NiO nanofibers.
Any suitable bandgap material is used as the p-layer including
nanofibers of any suitable pure metal oxides such as
CuInGaSe.sub.2.
[0348] In some instances, Indium Tin Oxide ("ITO") is one of the
most widely used transparent conducting oxides (e.g., as a solar
cell substrate). In some instances, ITO has a superior electrical
conductivity and optical transparency. In some instances, ITO is
easy to be deposit as a thin film. In one embodiment, the anode
comprises ITO nanofibers. In some instances, any suitable
conducting, transparent material is used as the anode including
nanofibers of any suitable pure inorganic materials such as
carbon.
[0349] In some embodiments, the cathode comprises Al, the n-layer
comprises ZnO, the photoactive layer comprises PbSe, the p-layer
comprises NiO, and the anode comprises ITO. In some embodiments,
any one or more of the components comprise nanofibers. In some
instances, the solar cells based on the nanofibers have good
connectivity among nanocrystals in each layer with minimal
recombination losses. In some instances, the solar cells based on
the nanofibers remove the complications associated with
incompatibility among processes for each component.
[0350] FIG. 37 illustrates an schematic of an embodiment of a solar
cell device using nanofibers provided herein.
Flexible Solar Cells
[0351] In some instances, inorganic solid-state junction devices
are being replaced by cells based on nanocrystalline and conducting
films (i.e., thin films). In some instances, thin-film structures
reduce the cost of photovoltaic devices (e.g., by eliminating the
use of the expensive silicon wafers). In some instances, it is now
possible to depart completely from solid-state junction devices, by
replacing the contacting phase to the semiconductor by an
electrolyte, liquid, gel or solid, thereby forming a
photo-electrochemical cell. In some instances, the prototype of
this family of devices is the dye-sensitized solar cell (see FIG.
41). In some instances, the dye-sensitized solar cell performs the
optical absorption and the charge separation processes by the
association of a sensitizer as light-absorbing material with a wide
band gap semiconductor of nanocrystalline morphology.
[0352] In one aspect, described herein are thin film solar cells
and photo-electrochemical cells comprising nanofibers. In various
aspects, the present disclosure includes thin film solar cells and
photo-electrochemical cells that include the nanofibers described
herein, includes thin film solar cells and photo-electrochemical
cells that include a nanofiber produced by the methods described
herein, and includes thin film solar cells and
photo-electrochemical cells that include a nanofiber produced by
the system described herein. In various aspects, described herein
are methods for making and methods for using thin film solar cells
and photo-electrochemical cells that include nanofibers.
[0353] In some instances, the thin film solar cells and
photo-electrochemical cells are flexible. In some instances, ITO
(Indium Tin Oxide) is not flexible. In some instances, various
flexible substrates based on transparent polymers have been
developed, but they do not provide enough thermal stability for
thermal treatment of electrode materials (>450.degree. C.) or
good adhesion between the substrate and electrodes. In some
embodiments, described herein are coaxial nanofibers of alumina
(core) and ITO (sheath) (e.g., for use as substrates for flexible
solar cell applications). In some embodiments, the alumina/ITO
nanofibers have good thermal stability and good adhesion between
the substrate and the electrodes.
[0354] In some instances, inorganic materials such as alumina,
alumina-magnesia and zirconia have been fabricated as flexible
substrates for catalytic applications. In some embodiments,
insertion of these flexible inorganic materials in the ITO sheath
of coaxial nanofibers results in improved flexibility without
losing transparency and conductivity. In some embodiments, such
coaxial nanofibers of alumina and ITO are synthesized via
water-based spinning (e.g., as substrates for flexible solar
cells). In some embodiments, the development of alumina/ITO
nanofibers cathodes is carried out in two steps. In some
embodiments, aqueous polymer solutions containing high loading of
Al precursor and ITO precursor are coaxially electrospun as core
and sheath layer, respectively, followed by the thermal treatment
to create alumina/ITO coaxial nanofibers.
[0355] In some embodiments, a high speed air stream is incorporated
into the coaxial procedure as an additional skin layer (i.e.,
tri-axial jets of alumina precursor (core)/ITO (middle)/air
(sheath)). In some embodiments, the gas flow produces nanofibers at
a faster rate. In some embodiments, (e.g., as shown in FIG. 43),
tri-axial electrospinning is utilized in the confined assembly of
block copolymers sandwiched by silica layers.
[0356] In various aspects, the present disclosure includes flexible
solar cells that include the nanofibers described herein, includes
flexible solar cells that include a nanofiber produced by the
methods described herein, and includes flexible solar cells that
include a nanofiber produced by the system described herein. In
some aspects, described herein are methods for making and methods
for using flexible solar cells that comprise nanofibers. In one
aspect, the disclosure includes solar cells comprising a substrate
comprising nanofibers comprising alumina, ITO, or a mixture of
alumina and ITO.
[0357] FIG. 42 shows the principle of operation of a thin film
nanocrystal/nanowire hybrid solar cell.
[0358] FIG. 44 shows a TEM image of tri-axial nanofibers of
SiO.sub.2 (core)/PI-b-PS with Fe.sub.3O.sub.4 (middle)/SiO.sub.2
(sheath).
Other Uses
[0359] In some instances, there are uses for the pure metal and/or
ceramic nanofibers other than in electrochemical devices (e.g.,
filters, sensors, catalysts, membranes, electrodes, tissue
regeneration matrixes, and the like).
[0360] Catalysis is the change in rate of a chemical reaction due
to the participation of a substance called a catalyst. In some
instances, unlike reagents that participate in the chemical
reaction, a catalyst is not consumed by the reaction itself. In
some instances, a catalyst participates in multiple chemical
transformations. In some instances, catalysts that speed the
reaction are called positive catalysts. In some instances,
substances that interact with catalysts to slow the reaction are
called inhibitors (or negative catalysts). In some instances,
substances that increase the activity of catalysts are called
promoters, and substances that deactivate catalysts are called
catalytic poisons.
[0361] In some instances, solid-state catalysts (sometimes known as
a heterogeneous catalyst) catalyze reactions on their surface.
Exemplary solid-state catalysts are metals and metal alloys. In
some instances, metals and metal alloys are expensive (e.g.,
precious metals) and reactions are surface-catalyzed. In some
instances, it is advantageous to use a catalyst with a high surface
to mass ratio (e.g., to maximize performance per cost). In some
instances, long, thin nanofibers have a high surface area to mass
ratio, so are a desirable material from which to make
catalysts.
[0362] In one aspect, described herein are catalysts. In various
aspects, the present disclosure includes a catalyst that comprises
the nanofibers described herein, includes a catalyst that comprises
a nanofiber produced by the methods described herein, and includes
a catalyst that comprises a nanofiber produced by the system
described herein. In some aspects, described herein are methods for
making and methods for using catalysts that comprise
nanofibers.
[0363] In some instances, hydrogen is an energy carrier suitable
for use in fuel cells. In one embodiment, the catalyst comprises
composite nanofibers comprising a first layer (e.g., comprising Fe
or Ni) and a second layer (e.g., comprising SiO.sub.2, ZrO.sub.2 or
Al.sub.2O.sub.3). In some embodiments, the catalyst is capable of
producing H.sub.2 from glucose or cellulose. In some embodiments,
the catalyst has a maximum temperature for H.sub.2 production of
about 60.degree. C. (e.g., increased from about 40.degree. C.).
[0364] In some instances, hydrogen sulfide is a poisonous gas that
is a pollutant in some industrial processes. In some instances,
hydrogen sulfide is removed by a catalyst. In some embodiments, the
catalyst comprises composite nanofibers (e.g., comprising ZnO on
ZrO.sub.2). In some embodiments, the catalyst is capable of
removing H.sub.2S from flue gas. In some embodiments, the catalyst
is capable of removing H.sub.2S to a concentration of 10 ppm.
[0365] In some instances, filters are used to purify particles from
a fluid stream. In one aspect, the present disclosure includes
filters. In various aspects, the present disclosure includes a
filter that comprises the nanofibers described herein, includes a
filter that includes a nanofiber produced by the methods described
herein, and includes a filter that includes a nanofiber produced by
the system described herein. In various aspects, described herein
are methods for making and methods for using filters that comprise
nanofibers.
[0366] In some embodiments, the filter is a water filter. In some
embodiments, the filter is an air filter. In some embodiments, the
filter is designed to remove particles of a certain size.
[0367] In some embodiments, the nanofibers described herein are
used in sensors. In one embodiment, the sensor comprises nanofibers
comprising metal oxides. In some embodiments, the metal oxides are
dispersed in a conducting metal. In some embodiments, a molecule is
sensed by a change in current. In one embodiment, the nanofiber
comprises V.sub.2O.sub.5 and the molecule is ammonia.
[0368] In one aspect, the present disclosure includes sensors. In
various aspects, the present disclosure includes a sensor that
comprises the nanofibers described herein, includes a sensor that
includes a nanofiber produced by the methods described herein, and
includes a sensor that includes a nanofiber produced by the system
described herein. In some embodiments, described herein are methods
for making and methods for using sensors that comprise
nanofibers.
[0369] In some instances, a membrane is a general or selective
barrier, which is often thin. In some instances, the nanofibers
described herein are formed into membranes. In one embodiment, the
membrane comprises nanofibers (e.g., SiO.sub.2 comprising metal
oxides). In some embodiments, the membrane is capable of removing
metal ions from wastewater. In some embodiments, the membrane
comprises nanofibers comprising TiO.sub.2. In some embodiments, the
membrane is capable of degrading organic pollutants. In various
embodiments, the pollutant is a pesticide or volatile organic
compound. In some instances, the degradation of the pollutant is
photocatalytic (i.e., catalyzed by light).
[0370] In one aspect, the present disclosure includes membranes. In
various aspects, the present disclosure includes a membrane that
comprises the nanofibers described herein, includes a membrane that
comprises a nanofiber produced by the methods described herein, and
includes a membrane that comprises a nanofiber produced by the
system described herein. In some aspects, described herein are
methods for making and methods for using membranes that comprise
nanofibers.
[0371] In some instances, an electrode is an electrical conductor
used to make contact with a nonmetallic part of a circuit (e.g., a
semiconductor, an electrolyte or a vacuum). In some instances,
electrodes are utilized in electrochemical devices (e.g., fuel
cells, batteries, ultra-capacitors and solar cells). In one aspect,
the present disclosure includes electrodes. In various aspects, the
present disclosure includes an electrode that comprises the
nanofibers described herein, includes an electrode that comprises a
nanofiber produced by the methods described herein, and includes an
electrode that comprises a nanofiber produced by the system
described herein. In some aspects, described herein are methods for
making and methods for using electrodes that comprise
nanofibers.
[0372] In some instances, the nanofibers are used in medicine,
including in tissue culture. In some embodiments, described herein
are tissue regeneration matrixes. For example, the nanofibers are
used for constructing a porous scaffold onto which cells are seeded
that grow to fill the scaffold (e.g., thereby producing a material
suitable for tissue supplementation or replacement).
[0373] In various aspects, the present disclosure includes an
electrode that comprises the nanofibers described herein, includes
an electrode that comprises a nanofiber produced by the methods
described herein, and includes an electrode that comprises a
nanofiber produced by the system described herein. In some aspects,
described herein are methods for making and methods for using
electrodes that comprise nanofibers.
[0374] While preferred embodiments of the present invention have
been shown and described herein, it will be obvious to those
skilled in the art that such embodiments are provided by way of
example only. Numerous variations, changes, and substitutions will
now occur to those skilled in the art without departing from the
invention. It should be understood that various alternatives to the
embodiments of the invention described herein may be employed in
practicing the invention. It is intended that the following claims
define the scope of the invention and that methods and structures
within the scope of these claims and their equivalents be covered
thereby.
EXAMPLES
Example 1
Preparing a Fluid Stock of Nickel Acetate and PVA
[0375] Two (2) grams of nickel acetate, the metal precursor, was
dissolved in 20 ml of 1 molar acetic acid solution. The solution
was stirred for 2 hours to create a solution of nickel acetate. The
solution was homogenous.
[0376] In a second solution, 1 gram of 99.7% hydrolyzed polyvinyl
alcohol (PVA) with an average molecular weight of 79 kDa and
polydispersity index of 1.5 was dissolved in 10 ml of de-ionized
water. The polymer solution was heated to a temperature of
95.degree. C. and stirred for 2 hours to create a homogenous
solution.
[0377] The nickel acetate solution was then combined with the PVA
solution to create a fluid stock. In order to distribute the
precursor substantially evenly in the fluid stock, the precursor
solution was added gradually to the polymer solution while being
continuously vigorously stirred for 2 hours. The mass ratio of
precursor to polymer for the fluid feed (based on initial nickel
acetate mass) was 2:1.
Example 2
Characterization of a Fluid Stock of Nickel Acetate and PVA
[0378] The chemical interaction between the ligand of the metal
precursor and the functional group in the polymer backbone resulted
in extremely high loading of metal precursors without losing the
spinnability. The interaction was demonstrated in the FT-IR study
for nanofibers with various ratios of PVA to Ni precursor. As
demonstrated in FIG. 2, the drastic reduction of --OH bond and
substantial increase in --CO bond were observed at high loading of
Ni precursor (Ni:PVA=4:1).
Example 3
Electrospinning a Fluid Stock of Nickel Acetate and PVA
[0379] The fluid stock of Example 1 was electrospun by a
gas-assisted technique. The overall process and apparatus is
depicted in FIG. 1. The fluid stock was loaded into a syringe pump
connected to a spinneret with an inner nozzle diameter (fluid
stock) of 4.13.times.10.sup.-4 m and an outer (air) diameter of
1.194.times.10.sup.-3 m. The distance between the nozzle and the
collection plate was kept at about 15 cm and the fluid stock was
spun at a rate of 0.1 ml/min. A charge of +15 kV was maintained at
the collector. The air velocity at the nozzle was 100 m/s. The
temperature of the air and fluid stock at the nozzle was 300 K.
Example 4
Calcinating a Fluid Feed of Nickel Acetate and PVA to Create a Pure
Nickel Nanofiber
[0380] The electrospun fluid stock of Example 3 was heated for 2
hours at 600.degree. C. in an atmosphere of 100% Ar gas. In order
to visualize the nanofiber before and after calcination an SEM
image was taken before and after calcination as depicted in FIG. 3.
The diameter of the nanofiber was approximately 500-700 nm as spun
and 400-500 nm after calcination. In order to characterize the
nanofiber after calcination, an x-ray diffraction measurement was
conducted a Scintag Theta-Theta X-ray Diffractometer, indicating
that the nanofiber was substantially pure nickel as depicted in
FIG. 3.
Example 5
Calcinating a Fluid Feed of Nickel Acetate and PVA to Create a
Nickel Oxide Nanofiber
[0381] The electrospun fluid stock of Example 3 was heated for 2
hours at 600.degree. C. in an atmosphere of air. In order to
visualize the nanofiber before and after calcination an SEM image
was taken before and after calcination as depicted in FIG. 4. The
diameter of the nanofiber was approximately 500-700 nm as spun and
300-500 nm after calcination. An x-ray diffraction measurement
indicates that that the nanofiber was substantially pure nickel
oxide as depicted in FIG. 4.
Example 6
Calcinating a Fluid Feed of Copper Acetate and PVA to Create a
Copper Nanofiber
[0382] Following the procedure of Example 1, a fluid stock of
copper acetate and PVA were prepared with the ratio of
precursor:polymer of 2:1. These fluid stocks were electrospun by
the procedure of Example 3. The electrospun fluid stock was heated
for 2 hours at 800.degree. C. in an atmosphere of 94% Ar and 6%
H.sub.2 gas. In order to visualize the nanofiber before and after
calcination an SEM image was taken before and after calcination as
depicted in FIG. 5. The diameter of the nanofiber was approximately
600-800 nm as spun and 300-500 nm after calcination. An x-ray
diffraction measurement indicates that that the nanofiber was
substantially pure copper as depicted in FIG. 5.
Example 7
Calcinating a Fluid Feed of Copper Acetate and PVA to Create a
Copper Oxide Nanofiber
[0383] The electrospun fluid stock of Example 6 was heated for 2
hours at 600.degree. C. in an atmosphere of air. In order to
visualize the nanofiber before and after calcination an SEM image
was taken before and after calcination as depicted in FIG. 6. The
diameter of the nanofiber was approximately 600-800 nm as spun and
200-600 nm after calcination. An x-ray diffraction measurement
indicates that that the nanofiber was substantially pure copper
oxide as depicted in FIG. 6.
Example 8
Calcinating a Fluid Feed of Silver Acetate and PVA to Create a
Silver Nanofiber
[0384] Following the procedure of Example 1, a fluid stock of
silver acetate and PVA were prepared with ratio of
precursor:polymer of 2:1. These fluid stocks were electrospun by
the procedure of Example 3. The electrospun fluid stock was heated
for 2 hours at 600.degree. C. in an atmosphere of air. In order to
visualize the nanofiber before and after calcination an SEM image
was taken before and after calcination as depicted in FIG. 7. The
diameter of the nanofiber was approximately 900-1200 nm as spun and
600-800 nm after calcination. An x-ray diffraction measurement
indicates that that the nanofiber was substantially pure silver as
depicted in FIG. 7.
Example 9
Calcinating a Fluid Feed of Iron Acetate and PVA to Create an Iron
Nanofiber
[0385] Following the procedure of Example 1, a fluid stock of iron
acetate and PVA were prepared with the ratio of precursor:polymer
of 2:1. These fluid stocks were electrospun by the procedure of
Example 3. The electrospun fluid stock was heated for 2 hours at
600.degree. C. in an atmosphere of air. In order to visualize the
nanofiber before and after calcination an SEM image was taken
before and after calcination as depicted in FIG. 8. The diameter of
the nanofiber was approximately 300-500 nm as spun and 200-400 nm
after calcination. An x-ray diffraction measurement indicates that
that the nanofiber was substantially pure iron as depicted in FIG.
8.
Example 10
Calcinating a Fluid Feed of Zinc Acetate and PVA to Create a Zinc
Oxide Nanofiber
[0386] Following the procedure of Example 1, a fluid stock of zinc
acetate and PVA were prepared with the ratio of precursor:polymer
of 2:1. These fluid stocks were electrospun by the procedure of
Example 3. The electrospun fluid stock was heated for 2 hours at
600.degree. C. in an atmosphere of air. In order to visualize the
nanofiber before and after calcination an SEM image was taken
before and after calcination as depicted in FIG. 9. The diameter of
the nanofiber was approximately 500-1000 nm as spun and 400-700 nm
after calcination. An x-ray diffraction measurement indicates that
that the nanofiber was substantially pure zinc oxide as depicted in
FIG. 9.
Example 11
Calcinating a Fluid Feed of Cadmium Acetate and PVA to Create a
Cadmium Nanofiber
[0387] Following the procedure of Example 1, a fluid stock of
cadmium acetate and PVA were prepared with the ratio of
precursor:polymer of 2:1. These fluid stocks were electrospun by
the procedure of Example 3. The electrospun fluid stock was heated
for 2 hours at 800.degree. C. in an atmosphere of air. In order to
visualize the nanofiber before and after calcination an SEM image
was taken before and after calcination as depicted in FIG. 10. The
diameter of the nanofiber was approximately 800-1200 nm as spun and
600-900 nm after calcination. An x-ray diffraction measurement
indicates that that the nanofiber was substantially pure cadmium as
depicted in FIG. 10.
Example 12
Calcinating a Fluid Feed of Zirconium Acetate and PVA to Create a
Zirconia Nanofiber
[0388] Following the procedure of Example 1, a fluid stock of
zirconium acetate and PVA were prepared with the ratio of
precursor:polymer of 2:1. These fluid stocks were electrospun by
the procedure of Example 3. The electrospun fluid stock was heated
for 2 hours at 800.degree. C. in an atmosphere of air or 94% Ar and
6% H.sub.2 gas. In order to visualize the nanofiber before and
after calcination an SEM image was taken before and after
calcination as depicted in FIG. 10. The diameter of the nanofiber
was approximately 800-1000 nm as spun and 300-600 nm after
calcination. An x-ray diffraction measurement indicates that that
the nanofiber was substantially pure zirconia as depicted in FIG.
11.
Example 13
Calcinating a Fluid Feed of Lead Acetate and PVA to Create a Lead
Nanofiber
[0389] Following the procedure of Example 1, a fluid stock of lead
acetate and PVA were prepared with the ratio of precursor:polymer
of 2:1. These fluid stocks were electrospun by the procedure of
Example 3. The electrospun fluid stock was heated for 2 hours at
600.degree. C. in an atmosphere of 94% Ar and 6% H.sub.2 gas. In
order to visualize the nanofiber before and after calcination an
SEM image was taken before and after calcination as depicted in
FIG. 10. The diameter of the nanofiber was approximately 500-1200
nm as spun and 250-700 nm after calcination. An x-ray diffraction
measurement indicates that that the nanofiber was substantially
pure lead as depicted in FIG. 12.
Example 14
Fluid Feeds and Nanofibers
[0390] Following the procedure of Example 1, fluid stocks are
prepared according to Table 2 in the identified
precursor-to-polymer load ratio (based on initial precursor mass
combined with the polymer). Nanofibers are prepared by calcination
under appropriate conditions.
TABLE-US-00002 TABLE 2 precursor polymer load ratio nanofiber iron
nitrate PVA 1:1 iron iron chloride PVA 2:1 steel (+carbon powder)
iron acetate PVE 1:1 stainless steel chromium acetate (89/11)
zirconium chloride PVA 2:1 zirconia nickel bromide PEO 1:1 nickel
oxide chromium methoxide PVE 1.5:1 chromium tungsten ethoxide PVA
3:1 tungsten CdClOH polyvinyl 1:1 cadmium oxide pyridine silver
acetate PEO 1:1 silver nickel nitrate polyacrylic 2:1 nickel acid
copper ethoxide PVA 1:1 copper nickel chloride PVE 3:1 nickel oxide
zirconium nitrate polyvinyl 1:1 zirconia pyridine copper nitrate
PVE 3.5:1 copper oxide nickel t-butoxide PVO 1:1 nickel copper
chloride polyacrylic 1.5:1 copper acid aluminum nitrate PVE 2:1
aluminum-zirconia zirconium acetate (70/30) composite
Example 15
Exploring the Loading of Nickel Acetates on PVA
[0391] Following the procedure of Example 1, various fluid stocks
of nickel acetate and PVA were prepared with ratios of
precursor:polymer of 1:2, 1:1, 2:1, and 4:1. These fluid stocks
were electrospun by the procedure of Example 3. At that point, 4
SEM micrographs were taken of the electrospun fluid stock. The
electrospun fluid stock was then calcinated by the procedure of
Example 4 to create pure Ni nanofibers. At that point, 4
micrographs were taken of the calcinated nanofibers. FIG. 13 shows
that the diameter of the nanofibers increased with higher loading
of precursor. It also shows that continuous, high-quality
nanofibers were formed, particularly at high loading of precursor.
TEM micrographs were also taken of the calcinated nanofibers. FIG.
14 shows that there are no voids in the nanofibers, confirming that
they are dense and coherent.
Example 16
Investigation of the Atomic Composition of a Pure Nickel
Nanofiber
[0392] Energy-dispersive x-ray spectroscopy (EDX) was used to
measure the elemental composition of a pure nickel nanofiber. FIG.
15 shows that for both dark (left) and bright (right) regions of
the TEM images, the majority of the nanofiber is Ni with a small
oxygen content. Negligible amounts of carbon are detected.
Example 17
Preparing a PbSe Alloy Nanofiber
[0393] A mixture of 50% Pb and 50% Se were formed from lead acetate
and Se powder according to the procedures of Example 1. The
precursors were further made into a fluid stock with PVA according
to the procedure of Example 1 and electrospun according to the
procedure of Example 3. The electrospun fluid stock was calcinated
by heating for 2 hours at 600.degree. C. in an atmosphere of 100%
Ar. Micrographs (FIG. 23) show continuous metal alloy nanofibers
and TEM micrographs (FIG. 24) show that they are dense and
coherent.
Example 18
Investigation of the Atomic Composition of a PbSe Alloy
Nanofiber
[0394] Energy-dispersive x-ray spectroscopy (EDX) was used to
measure the elemental composition of the PbSe alloy nanofiber
produced in Example 17. FIG. 25 shows that for both dark (left) and
bright (right) regions of the TEM images, the composition of Pb to
Se is maintained as relatively equal. Negligible amounts of carbon
are detected.
Example 19
Investigation of the Electrical Conductivities of Pure Metal
Nanofibers
[0395] A two point probe was used to measure the electric
conductivity of various pure metal nanofiber mats obtained via
three different thermal treatment conditions (low temperature
(400.degree. C.) treatment under inert atmosphere (Treatment Scheme
1), low temperature treatment under air and then under inert
atmosphere (Treatment Scheme 2), and high temperature (800.degree.
C.) treatment under inert atmosphere (Treatment Scheme 3). FIG. 30
shows that calcinated pure metal nanofibers prepared by the methods
of the disclosure (Treatment Scheme 2 and 3) exhibit very high
conductivity (greater than 10.sup.6 S/m) and are nearly as
conductive as the known conductivity of the metal when formed into
a sheet. On the contrary, metal fibers with Treatment Scheme 1 and
from low precursor loading exhibit much lower conductivity (lower
than 10.sup.3 S/m).
Example 20
Preparing a ZrO.sub.2/Ni Hybrid Nanofiber
[0396] Fluid feeds of Zr acetate and Ni acetate were prepared
according to the procedure of Example 1. The two fluid stocks were
then electrospun in a co-axial manner using a spinneret similar to
the one depicted in FIG. 35. The center conduit contained Ni
acetate fluid stock (not air as depicted in FIG. 35) and the outer
conduit contained ZrO.sub.2 fluid stock. The electrospinning
procedure was gas-assisted. The electrospun hybrid fluid stock was
calcinated by heating for 2 hours at 600.degree. C. in an
atmosphere of air, followed by 2 hours at 600 C in an atmosphere of
94% Ar and 6% H.sub.2 gas. Micrographs (FIG. 31) show continuous
metal alloy nanofibers and TEM micrographs (FIG. 32) show that they
are dense and coherent.
Example 21
Investigation of the Atomic Composition of a ZrO.sub.2/Ni Hybrid
Nanofiber
[0397] Energy-dispersive x-ray spectroscopy (EDX) was used to
measure the elemental composition of the ZrO.sub.2/Ni hybrid
nanofiber produced in Example 20. FIG. 33 shows that the dark
(left) and bright (right) regions of the TEM images have different
compositions. There is much more nickel in the center (left, dark)
than on the exterior (right, light). Furthermore, the EDAX shows
that the ratio of Zr to O was 1:2 for both cases, indicated the
formation of ZrO.sub.2.
Example 22
Fuel Cells Electrodes
[0398] Disclosed herein are fuel cell electrodes that include
Fe--Pt nanofibers. These nanofibers may be prepared according to
the procedures and system depicted in FIG. 34. Water-soluble Fe and
Pt acetates are mixed with a water-soluble polymer such as PVA to
create a fluid stock as in Example 1. The ratio of precursor to
polymer is 4:1 in this example. In addition, gas assisted
electrospinning will be adapted to increase the throughput. We have
demonstrated that the nanofiber production rate can be increased by
more than ten times by incorporate air flow into the sheath jet
layer in a coaxial scheme. As depicted in FIG. 34, the spinning
dope can be prepared by adding an adequate ratio of Fe to Pt
precursors to aqueous polymer solution and is used as the core jet
in coaxial electrospinning, while a high-speed air stream is used
as the sheath layer jet to stretch the core jet of precursor
solution. The creation of the face-centered tetragonal structure of
Fe--Pt is pursued to enhance oxygen reduction and durability under
the minimized Pt loading.
Example 23
Hollow Si or Ge Nanofibers Suitable for Lithium Ion Battery
Anodes
[0399] FIG. 35 shows an apparatus suitable for producing hollow Si
or Ge nanofibers suitable for use as anodes in lithium ion
batteries. The high speed air and Si or Ge precursor solution form
the core and sheath jets in gas-assisted coaxial
electrospinning
Example 24
Al.sub.2O.sub.3/ITO Hybrid Nanofibers Suitable for Use in Flexible
Solar Cells
[0400] FIG. 36 shows a schematic of the process and system for
producing Al.sub.2O.sub.3/ITO hybrid nanofibers suitable for use in
flexible solar cells. Triaxial configuration of
Al.sub.2O.sub.3/ITO/air in gas-assisted electrospinning is utilized
to produce a coaxial Al.sub.2O.sub.3/ITO nanofiber. FIG. 37 shows
micrographs, x-ray diffraction plots and a schematic for a solar
cell with a plurality of components made from nanofibers.
Example 25
Further Examples of Nanofibers
[0401] In one aspect, described herein are various nanofibers
comprising metal, ceramic, metal alloy, and combinations thereof.
In one aspect, described herein are methods for producing various
nanofibers comprising metal, ceramic, metal alloy, and combinations
thereof. For example: FIG. 16 shows micrographs and an x-ray
diffraction plot of ZnO/ZrO.sub.2 hybrid nanofibers; FIG. 17 shows
micrographs and an x-ray diffraction plot of Ag/ZrO.sub.2 hybrid
nanofibers; FIG. 18 shows micrographs and an x-ray diffraction plot
of Ni/ZrO.sub.2 hybrid nanofibers; FIG. 19 shows micrographs and an
x-ray diffraction plot of Fe/ZrO.sub.2 hybrid nanofibers; FIG. 21
shows micrographs and an x-ray diffraction plot of
Ni/Al.sub.2O.sub.3 hybrid nanofibers; FIG. 22 shows micrographs and
an x-ray diffraction plot of CdSe alloy nanofibers; FIG. 26 shows
micrographs and an x-ray diffraction plot of CdTe alloy nanofibers;
FIG. 27 shows micrographs and an x-ray diffraction plot of PbTe
alloy nanofibers; FIG. 28 shows micrographs and an x-ray
diffraction plot of Fe.sub.3O.sub.4/FeNi alloy nanofibers; and FIG.
29 shows TEM micrographs of Fe.sub.3O.sub.4/FeNi alloy nanofibers.
In other aspects, processes describe in the examples herein were
utilized to make the nanofibers of Table 1.
[0402] FIG. 20 shows TEM micrographs of various hybrid
nanofibers.
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