U.S. patent application number 14/040406 was filed with the patent office on 2014-06-26 for process for making silver nanostructures and copolymer useful in such process.
This patent application is currently assigned to Rhodia Operations. The applicant listed for this patent is Rhodia Operations. Invention is credited to Ahmed Alsayed, Chantal Badre, Lawrence Hough.
Application Number | 20140178247 14/040406 |
Document ID | / |
Family ID | 50389153 |
Filed Date | 2014-06-26 |
United States Patent
Application |
20140178247 |
Kind Code |
A1 |
Alsayed; Ahmed ; et
al. |
June 26, 2014 |
PROCESS FOR MAKING SILVER NANOSTRUCTURES AND COPOLYMER USEFUL IN
SUCH PROCESS
Abstract
A process for making silver nanostructures, which includes the
step of reacting at least one polyol and at least one silver
compound that is capable of producing silver metal when reduced, in
the presence of: (a) a source of chloride or bromide ions, and (b)
at least one copolymer that comprises: (i) one or more first
constitutional repeating units that each independently comprise at
least one pendant saturated or unsaturated, five-, six-, or
seven-membered, acylamino- or diacylamino-containing heterocylic
ring moiety per constitutional repeating unit, and (ii) one or more
second constitutional repeating units, each of which independently
differs from the one or more first nonionic constitutional
repeating units, and has a molecular weight of greater than or
equal to about 500 grams per mole, is described herein.
Inventors: |
Alsayed; Ahmed; (Cherry
Hill, NJ) ; Hough; Lawrence; (Philadephia, PA)
; Badre; Chantal; (Guttenberg, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Rhodia Operations |
Aubervilliers |
|
FR |
|
|
Assignee: |
Rhodia Operations
Aubervilliers
FR
|
Family ID: |
50389153 |
Appl. No.: |
14/040406 |
Filed: |
September 27, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61706280 |
Sep 27, 2012 |
|
|
|
Current U.S.
Class: |
420/501 ;
526/264; 75/343 |
Current CPC
Class: |
Y10S 977/762 20130101;
B22F 2009/245 20130101; B22F 2304/05 20130101; Y10S 977/932
20130101; B82Y 30/00 20130101; H01B 1/124 20130101; B22F 9/24
20130101; B22F 9/18 20130101; B22F 2301/255 20130101; B22F 1/0003
20130101; B22F 1/0044 20130101; B82Y 40/00 20130101; C08F 226/10
20130101; Y10S 977/896 20130101; H01B 1/02 20130101; C08F 226/10
20130101; C08F 226/04 20130101 |
Class at
Publication: |
420/501 ;
526/264; 75/343 |
International
Class: |
C08F 226/10 20060101
C08F226/10; B22F 9/18 20060101 B22F009/18 |
Claims
1. A process for making silver nanostructures, comprising reacting
at least one polyol and at least one silver compound that is
capable of producing silver metal when reduced, in the presence of:
(a) a source of chloride or bromide ions, and (b) at least one
copolymer that comprises: (i) one or more first constitutional
repeating units that each independently comprise at least one
pendant saturated or unsaturated, five-, six-, or seven-membered,
acylamino- or diacylamino-containing heterocylic ring moiety per
constitutional repeating unit, and (ii) one or more second
constitutional repeating units, each of which independently differs
from the one or more first nonionic constitutional repeating units,
and has a molecular weight of greater than or equal to about 500
grams per mole.
2. The process of claim 1, wherein the first constitutional
repeating units of the copolymer each independently comprise a
pyrrolidonyl moiety or a pyrrolidinedionyl moiety and the second
constitutional repeating units of the copolymer each independently
comprise a cationic moiety.
3. The process of claim 2, wherein, wherein the copolymer is a
random copolymer made by free radical polymerization of vinyl
pyrrolidone, vinyl caprolactam, or vinyl pyrrolidone and vinyl
caprolactam with one or more ethylenically unsaturated cationic
monomers.
4. The process of claim 3, wherein the one or more ethylenically
unsaturated cationic monomers are selected from dimethylaminomethyl
(meth)acrylate, dimethylaminopropyl (meth)acrylate,
di(t-butyl)aminoethyl (meth)acrylate, dimethylaminomethyl
(meth)acrylamide, dimethylaminoethyl (meth)acrylamide,
dimethylaminopropyl (meth)acrylamide, vinylamine, vinyl imidazole,
vinylpyridine, vinylpyrrolidine, vinylpyrroline, vinylpyrazolidine,
vinylpyrazoline, vinylpiperidine, vinylpiperazine, vinylpyridine,
vinylpyrazine, vinylpyrimadine, vinylpyridazine, trimethylammonium
ethyl (meth)acrylate salts, dimethylammonium ethyl (meth)acrylate
salts, dimethylbenzylammonium (meth)acrylate salts, benzoylbenzyl
dimethylammonium ethyl(meth)acrylate salts, trimethyl ammonium
ethyl (meth)acrylamido salts, trimethyl ammonium propyl
(meth)acrylamido salts, vinylbenzyl trimethyl ammonium salts, and
diallyldimethyl ammonium salts.
5. The process of claim 4, wherein the copolymer is a random
copolymer made by free radical polymerization of a monomer mixture
comprising from about 80 to less than 100 parts by weight of vinyl
pyrrolidone and from greater than 0 to about 20 parts by weigh of a
diallyldimethylammonium salt.
6. The process of claim 1, wherein the at least one silver compound
comprises silver nitrate, the at least one polyol comprises
ethylene glycol, the total amount of silver nitrate added to the
reaction mixture is from 1.5.times.10.sup.-2 mole to about 1 mole
silver nitrate per Liter of reaction mixture, and the reaction is
conducted in the presence of, based on the weight of the reaction
mixture, from about 0.1 wt % to about 20 wt % of the copolymer.
7. Silver nanostructures made by the process of claim 1.
8. A copolymer, comprising, based on 1000 constitutional repeating
units of the copolymer: from 800 to 999 first constitutional
repeating units, each independently comprising at least one pendant
saturated or unsaturated, five-, six-, or seven-membered,
acylamino- or diacylamino-containing heterocylic ring moiety per
constitutional repeating unit, and from 1 to 200 second
constitutional repeating units, each independently comprising at
least one pendant organic moiety per unit that: (i) is selected
from ionic organic moieties and nonionic organic moieties, and (ii)
is not a saturated or unsaturated, five-, six-, or seven-membered,
acylamino- or diacylamino-containing heterocylic ring moiety, and
having a molecular weight of greater than or equal to about 500
grams per mole.
9. The copolymer of claim 8, wherein the second repeating units
each independently comprise at least one pendant organic moiety per
unit that is selected from cationic organic moieties.
10. The copolymer of claim 9, wherein, the copolymer is a random
copolymer made by free radical polymerization of vinyl pyrrolidone,
vinyl caprolactam, or vinyl pyrrolidone and vinyl caprolactam with
one or more ethylenically unsaturated cationic monomers.
11. The copolymer of claim 10, wherein the one or more
ethylenically unsaturated cationic monomers are selected from
dimethylaminomethyl (meth)acrylate, dimethylaminopropyl
(meth)acrylate, di(t-butyl)aminoethyl (meth)acrylate,
dimethylaminomethyl (meth)acrylamide, dimethylaminoethyl
(meth)acrylamide, dimethylaminopropyl (meth)acrylamide, vinylamine,
vinyl imidazole, vinylpyridine, vinylpyrrolidine, vinylpyrroline,
vinylpyrazolidine, vinylpyrazoline, vinylpiperidine,
vinylpiperazine, vinylpyridine, vinylpyrazine, vinylpyrimadine,
vinylpyridazine, trimethylammonium ethyl (meth)acrylate salts,
dimethylammonium ethyl (meth)acrylate salts, dimethylbenzylammonium
(meth)acrylate salts, benzoylbenzyl dimethylammonium
ethyl(meth)acrylate salts, trimethyl ammonium ethyl
(meth)acrylamido salts, trimethyl ammonium propyl (meth)acrylamido
salts, vinylbenzyl trimethyl ammonium salts, and diallyldimethyl
ammonium salts.
12. The copolymer of claim 10, wherein the copolymer is a random
copolymer made by free radical polymerization of a monomer mixture
comprising from about 800 to less than 1000 parts by weight of
vinyl pyrrolidone and from greater than 0 to about 200 parts by
weigh of a diallyldimethylammonium salt.
13. The process of claim 1, wherein the at least one polyol has a
pH of from about 1 to about 14.
14. The process of claim 1, wherein the at least one polyol has a
pH of from about 5 to about 12.
15. The process of claim 1, wherein the at least one polyol has a
pH of from about 7 to about 10.
16. A process for making silver nanostructures, comprising reacting
at least one polyol and at least one silver compound that is
capable of producing silver metal when reduced, in the presence of:
(a) a source of chloride or bromide ions, and (b) at least one
copolymer that comprises: (i) one or more first constitutional
repeating units that each independently comprise at least one
pendant saturated or unsaturated, five-, six-, or seven-membered,
acylamino- or diacylamino-containing heterocylic ring moiety per
constitutional repeating unit, and (ii) one or more second
constitutional repeating units, each of which independently differs
from the one or more first nonionic constitutional repeating units,
and has a molecular weight of greater than or equal to about 500
grams per mole; and (c) at least one base.
17. The process of claim 16, wherein the at least one base
comprises sodium hydroxide, lithium hydroxide, potassium hydroxide,
or mixtures thereof.
18. Silver nanostructures made by the process of claim 16.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a U.S. non-provisional application,
which claims the benefit of U.S. provisional application No.
61/706,280 filed Sep. 27, 2012, the entirety of which is hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a process for making silver
nanostructures and a copolymer useful in such process.
BACKGROUND
[0003] Transparent conductors, such as Indium Tin Oxide (ITO),
combine the electrical conductivity of metal with the optical
transparency of glass and are useful as components in electronic
devices, such as in display devices. Flexibility is likely to
become a broader challenge for ITO, which does not seem well suited
to the next generation of display, lighting, or photovoltaic
devices. These concerns have motivated a search for replacements
using conventional materials and nanomaterials. There is variety of
technical approaches for developing ITO substitutes and there are
four areas in which the alternative compete: price, electrical
conductivity, optical transparency, and physical resiliency.
[0004] Electrically conductive polymers, such as polythiophene
polymers, particularly a polymer blend of
poly(3,4-ethylenedioxythiophene) and poly(styrene sulfonate)
("PEDOT-PSS") have been investigated as possible alternatives to
ITO. The electrical conductivity of electrically conductive
polymers is typically lower than that of ITO, but can be enhanced
through the use of conductive fillers and dopants.
[0005] Processes for making electrically conductive metal
nanostructures are known. Ducamp-Sanguesa, et. al., Synthesis and
Characterization of Fine and Monodisperse Silver Particles of
Uniform Shape, Journal of Solid State Chemistry 100, 272-280 (1992)
and U.S. Pat. No. 7,585,349, issued Sep. 8, 2009, to Younan Xia,
et. al., each describe synthesis of silver nanowires by reduction
of a silver compound in a glycol in the presence of
polyvinylpyrrolidone.
[0006] Structures comprising a network of silver nanowires
encapsulated in an electrically conductive polymer have been
described. U.S. Patent Application Publication No. 2008/0259262
describes forming such structures by depositing a network of metal
nanowires on a substrate and then forming a conductive polymeric
film in situ, e.g., by electrochemical polymerization using the
metal nanowire network as an electrode. U.S. Patent Application
Publication No. 2009/0129004 describes forming such structures by
filtration of a silver nanowire dispersion to form a silver
nanowire network, heat treating the network, transfer printing the
heat treated network, and encapsulating the transfer printed
network with polymer.
[0007] The performance of such electrically conductive
polymer/silver nanowire composite films is, in some cases,
comparable to that of ITO but the processing required to obtain
composite films that exhibit that level of performance is quite
demanding, for example, the above described films require
processing steps, such as thermal treatment and compression, in
order to ensure that sufficient electrical connections are made
among the electrically conductive nanowires of the composite film
to provide a film having high conductivity and transparency. There
is an ongoing unresolved interest in increasing the electrical
conductivity and optical transparency of electrically conductive
polymer films.
SUMMARY OF THE INVENTION
[0008] In a first aspect, the present invention is directed to a
process for making silver nanostructures, comprising reacting at
least one polyol and at least one silver compound that is capable
of producing silver metal when reduced, in the presence of: [0009]
(a) a source of chloride or bromide ions, and [0010] (b) at least
one copolymer that comprises: [0011] (i) one or more first
constitutional repeating units that each independently comprise at
least one pendant saturated or unsaturated, five-, six-, or
seven-membered, acylamino- or diacylamino-containing heterocylic
ring moiety per constitutional repeating unit, and [0012] (ii) one
or more second constitutional repeating units, each of which
independently differs from the one or more first nonionic
constitutional repeating units, [0013] and has a molecular weight
of greater than or equal to about 500 grams per mole.
[0014] In a second aspect, the present invention is directed to a
copolymer, comprising, based on 1000 constitutional repeating units
of the copolymer:
[0015] from 800 to 999 first constitutional repeating units, each
independently comprising at least one pendant saturated or
unsaturated, five-, six-, or seven-membered, acylamino- or
diacylamino-containing heterocylic ring moiety per constitutional
repeating unit, and
[0016] from 1 to 200 second constitutional repeating units, each
independently comprising at least one pendant organic moiety that:
(i) is selected from ionic organic moieties and nonionic organic
moieties, and (ii) is not a saturated or unsaturated, five-, six-,
or seven-membered, acylamino- or diacylamino-containing heterocylic
ring moiety,
and having a molecular weight of greater than or equal to about 500
grams per mole.
[0017] In a third aspect, the present invention is directed to a
process for making silver nanostructures, comprising reacting at
least one polyol and at least one silver compound that is capable
of producing silver metal when reduced, in the presence of: [0018]
(a) a source of chloride or bromide ions, and [0019] (b) at least
one copolymer that comprises: [0020] (i) one or more first
constitutional repeating units that each independently comprise at
least one pendant saturated or unsaturated, five-, six-, or
seven-membered, acylamino- or diacylamino-containing heterocylic
ring moiety per constitutional repeating unit, and [0021] (ii) one
or more second constitutional repeating units, each of which
independently differs from the one or more first nonionic
constitutional repeating units, [0022] and has a molecular weight
of greater than or equal to about 500 grams per mole; and [0023]
(c) at least one base.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIGS. 1(a) and 1(b) show representative 1H NMR and FTIR
spectra of the poly(vinylpyrrolidone-co-diallyldimethylammonium
nitrate) random copolymers ("poly(VP-co-DADMAN)" copolymers) of
Examples 1A-1E.
[0025] FIG. 2 shows characteristics of the silver nanostructures of
Examples 2A-2G and Comparative Examples C1-C3, as a function of the
amount of silver nitrate added and the composition of the polymeric
protectant, wherein each cross corresponds to one of the
Examples.
[0026] FIG. 3 shows length distributions of the nanowire products
obtained using poly(VP-co-DADMAN) copolymer with 16 percent by
weight ("wt %") DADMAN content at different concentrations of
silver nitrate.
[0027] FIG. 4 shows arithmetic average length distribution of
nanowire products obtained using poly(VP-co-DADMAN) copolymer with
1 wt % DADMAN content at different concentrations of the copolymer
at two different amounts of silver nitrate.
[0028] FIG. 5 shows the titration curve of the "Lot A" ethylene
glycol used in Examples 2, 3, 4, and comparative examples
C2A-C2C.
[0029] FIG. 6 shows a TEM image of the silver nanowires of Example
2A.
[0030] FIG. 7 shows the titration curve of the "Lot B" ethylene
glycol used in Examples 7, 8, and 9.
[0031] FIG. 8 shows an SEM image of the silver nanowires of Example
7 produced with the addition of lithium hydroxide.
[0032] FIG. 9 shows an image of the silver nanowires of Example 7
produced with the addition of lithium hydroxide as seen with an
optical microscope.
[0033] FIG. 10 shows an image of the silver nanowires of Example 8
produced with the addition of potassium hydroxide as seen with an
optical microscope.
[0034] FIG. 11 shows an image of the silver nanowires of Example 9
produced with the addition of sodium hydroxide as seen with an
optical microscope.
DETAILED DESCRIPTION OF THE INVENTION
[0035] As used herein, the following terms have the following
meanings:
[0036] "doped" as used herein in reference to an electrically
conductive polymer means that the electrically conductive polymer
has been combined with a polymeric counterion for the electrically
conductive polymer, which polymeric counterion is referred to
herein as "dopant", and is typically a polymeric acid, which is
referred to herein as a "polymeric acid dopant",
[0037] "doped electrically conductive polymer" means a polymer
blend comprising an electrically conductive polymer and a polymeric
counterion for the electrically conductive polymer,
[0038] "electrically conductive polymer" means any polymer or
polymer blend that is inherently or intrinsically, without the
addition of electrically conductive fillers such as carbon black or
conductive metal particles, capable of electrical conductivity,
more typically to any polymer or oligomer that exhibits a bulk
specific conductance of greater than or equal to 10.sup.-7 Siemens
per centimeter ("S/cm"), unless otherwise indicated, a reference
herein to an "electrically conductive polymer" include any optional
polymeric acid dopant,
[0039] "electrically conductive" includes conductive and
semi-conductive,
[0040] "electronic device" means a device that comprises one or
more layers comprising one or more semiconductor materials and
makes use of the controlled motion of electrons through the one or
more layers,
[0041] "layer" as used herein in reference to an electronic device,
means a coating covering a desired area of the device, wherein the
area is not limited by size, that is, the area covered by the layer
can, for example, be as large as an entire device, be as large as a
specific functional area of the device, such as the actual visual
display, or be as small as a single sub-pixel.
[0042] As used herein, the following terms have the following
meanings:
[0043] "alkyl" means a monovalent straight, branched or cyclic
saturated hydrocarbon radical, more typically, a monovalent
straight or branched saturated (C.sub.1-C.sub.40)hydrocarbon
radical, such as, for example, methyl, ethyl, n-propyl, isopropyl,
n-butyl, isobutyl, tert-butyl, hexyl, octyl, hexadecyl, octadecyl,
eicosyl, behenyl, tricontyl, and tetracontyl,
[0044] "cycloalkyl" means a saturated hydrocarbon radical, more
typically a saturated (C.sub.5-C.sub.22) hydrocarbon radical, that
includes one or more cyclic alkyl rings, which may optionally be
substituted on one or more carbon atoms of the ring with one or two
(C.sub.1-C.sub.6)alkyl groups per carbon atom, such as, for
example, cyclopentyl, cycloheptyl, cyclooctyl,
[0045] "heteroalkyl" means an alkyl group wherein one or more of
the carbon atoms within the alkyl group has been replaced by a
hetero atom, such as nitrogen, oxygen, or sulfur,
[0046] "heterocyclic" means an cyclic hydrocarbon group in which
one or more of the ring carbon atoms has been replaced by a hetero
atom, such as nitrogen, oxygen, or sulfur,
[0047] "alkylene" refers to a divalent alkyl group including, for
example, methylene, and poly(methylene),
[0048] "alkenyl" means an unsaturated straight or branched
hydrocarbon radical, more typically an unsaturated straight,
branched, (C.sub.2-C.sub.22) hydrocarbon radical, that contains one
or more carbon-carbon double bonds, including, for example,
ethenyl, n-propenyl, and iso-propenyl,
[0049] "aryl" means an unsaturated hydrocarbon radical that
contains one or more six-membered carbon rings in which the
unsaturation may be represented by three conjugated carbon-carbon
double bonds, wherein one or more of the ring carbons may be
substituted with one or more hydroxy, alkyl, alkenyl, alkoxy, halo,
or alkylhalo substituents, such as, for example, phenyl,
methylphenyl, trimethylphenyl, nonylphenyl, chlorophenyl,
trichloromethylphenyl, naphthyl, and anthryl, and
[0050] "aralkyl" means an alkyl group substituted with one or more
aryl groups, more typically a (C.sub.1-C.sub.18)alkyl substituted
with one or more (C.sub.6-C.sub.14)aryl substituents, such as, for
example, phenylmethyl, phenylethyl, and triphenylmethyl, and
[0051] "(C.sub.x-C.sub.y)" in reference to an organic group,
wherein x and y are each integers, means that the group may contain
from x carbon atoms to y carbon atoms per group.
[0052] Addition of the prefix "(meth)" to a group name, such as
"acrylate", "acrylic", "acrylamide", "acrylamido", or "allyl" to
form terms such as "(meth)acrylate, "(meth)acrylic",
"(meth)acrylamide, "(meth)acrylamido", and "(meth)allyl" is used
herein to indicate the methyl-substituted and/or the
non-methyl-substituted homologs of such groups. For example, the
term "ethyl (meth)acrylate", as used herein means ethyl acrylate,
ethyl methacrylate, or a mixture thereof.
[0053] As used herein in reference to an organic or inorganic
moiety, the following terms have the following meanings:
[0054] "cationic" means that the moiety carries a net positive
electrical charge,
[0055] "anionic" means that the moiety carries a net negative
electrical charge,
[0056] "amphoteric" and "zwitterionic" mean that the moiety has no
net electrical charge, but carries, or under certain pH conditions,
may carry both a localized negative electrical charge and a
localized positive electrical charge, and
[0057] "nonionic" means that the moiety is carries no net
electrical charge no localized negative electrical charge and no
localized positive electrical charge.
[0058] As used herein in reference to a polymer or copolymer
molecule, the following terms have the following meanings:
[0059] "constitutional repeating unit" means the smallest
constitutional unit, the repetition of which constitutes a chain or
a block of the polymer or copolymer molecule,
[0060] "constitutional unit" means an atom or group of atoms,
including pendant atoms or groups, if any, comprising a part of the
essential structure of the polymer or copolymer molecule or of a
block or chain of the polymer or copolymer molecule,
[0061] "chain" means the whole or a portion of the polymer or
copolymer molecule, comprising a linear or branched sequence of one
or more constitutional units between two boundary constitutional
units, each of which may be either an end-group, a branch point or
an otherwise-designated characteristic feature of the polymer or
copolymer molecule, and
[0062] "block" means, in reference to a copolymer, a portion of the
copolymer, comprising two or more constitutional units that has at
least one feature which is not present in the adjacent portions of
the copolymer.
[0063] The dimensions referred to herein in regard to bulk
nanostructure materials are averaged dimensions obtained by
sampling individual nanostructures contained in the bulk material
wherein the lengths are obtained using optical microscopy, and the
diameters are determined using electron microscopy. Using this
process, a sample of about 150 nanostructures are measured to
determine the lengths, and a sample of about 10 nanostructures are
measured to determine the diameters. An average diameter, average
length, and average aspect ratio are then determined for the
nanostructures examined as follows. Unless otherwise indicated,
nanostructure dimensions are given as arithmetic averages of the
measured nanowire population. In the case of anisotropic
nanostructures, such as nanowires, lengths may also be given as
length weighted average lengths, as determined by first taking the
length of each nanowire and dividing it by the sum of the lengths
of all nanowires measured to derive a quantity W.sub.1, which is
the percent contribution of the single nanowire to the sum length
of all nanowires, then, for each of the measured nanowires,
deriving a weighted length by multiplying the length of the
nanowire by its respective W.sub.1 value, and finally taking the
arithmetic average of the weighted lengths of the measured
nanowires to derive the length weighted average length of the
nanowire population. Aspect ratios of anisotropic nanostructures
are determined by dividing the length weighted average length of
the nanowire population by the average diameter of the anisotropic
nanostructure population.
[0064] As used herein, the term "nanostructures" generally refers
to nano-sized structures, at least one dimension of which is less
than or equal to 2000 nm, more typically less than or equal to 500
nm, even more typically, less than or equal to 250 nm, or less than
or equal to 100 nm, or less than or equal to 50 nm, or less than or
equal to 25 nm. The anisotropic electrically conductive
nanostructures can be of any anisotropic shape or geometry. As used
herein, the terminology "aspect ratio" in reference to a structure
means the ratio of the structure's longest characteristic dimension
to the structure's next longest characteristic dimension. In one
embodiment, the anisotropic electrically conductive nanostructures
have an elongated shape with a longest characteristic dimension,
i.e., a length, and a next longest characteristic dimension, i.e.,
a width or diameter, with an aspect ratio of greater than 1.
[0065] The at least one polyol serves as liquid medium in which to
conduct the reaction and as a reducing agent that reduces the
silver compound to silver metal. Suitable polyols are organic
compounds having a core moiety comprising at least 2 carbon atoms,
which may optionally further comprise one or more heteroatoms
selected from N and O, wherein the core moiety is substituted with
at least 2 hydroxyl groups per molecule and each hydroxyl group is
attached to a different carbon atom of the core moiety. Suitable
polyols are known and include, for example, alkylene glycols, such
as ethylene glycol, propylene glycols, and butanediols, alkylene
oxide oligomers, such as diethylene glycol, triethylene glycol,
tetraethylene glycol, dipropylene glycol, and polyalkylene glycols,
such as polyethylene glycol and polypropylene glycol, provided that
such polyalkylene glycol is liquid at the reaction temperature,
triols, such as, for example, glycerol, trimethylolpropane,
triethanolamine, and trihydroxymethylaminomethane, and compounds
having more than 3 hydroxyl groups per molecule, as well as
mixtures of two or more of any of such compounds. In one
embodiment, the polyol comprises ethylene glycol.
[0066] Suitable silver compounds that are capable of producing
silver metal when reduced are known and include silver oxide,
silver hydroxide, organic silver salts, and inorganic silver salts,
such as silver nitrate, silver nitrite, silver sulfate, silver
halides such as silver chloride, silver carbonates, silver
phosphate, silver tetrafluoroborate, silver sulfonate, silver
carboxylates, such as, for example, silver formate, silver acetate,
silver propionate, silver butanoate, silver trifluoroacetate,
silver acetacetonate, silver lactate, silver citrate, silver
glycolate, silver tosylate, silver tris(dimethylpyrazole)borate, as
well as mixtures of two or more of such compounds. In one
embodiment, the silver compound capable of producing silver metal
when reduced comprises silver nitrate (AgNO.sub.3).
[0067] Suitable sources of chloride and/or bromide ions include
hydrochloric acid, chloride salts, such as ammonium chloride,
calcium chloride, ferric chloride, lithium chloride, potassium
chloride, sodium chloride, triethylbenzyl ammonium chloride,
tetrabutyl ammonium chloride, hydrobromic acid, and bromide salts,
such as ammonium bromide, calcium bromide, ferric bromide, lithium
bromide, potassium bromide, sodium bromide, triethylbenzyl ammonium
bromide, tetrabutyl ammonium bromide, or, in a case wherein the
copolymer comprises a chloride or bromide counterion, the chloride
or bromide counterion of the copolymer. In one embodiment, the
source of chloride ions comprises lithium chloride.
[0068] In one embodiment, the source of chloride or bromide ions
comprises silver chloride and/or silver bromide, which may be added
to the reaction mixture in the form of colloidal particles. The
colloidal particles of silver chloride and/or silver bromide may
have a particle size of from about 10 nm to about 10 .mu.m, more
typically of from about 50 nm to about 10 .mu.m.
[0069] The pH of the at least one polyol may be any pH at room
temperature (25.degree. C.). The pH of the at least one polyol may
be determined by conventional analytical methods known in the art,
including, for example, colorimetric titration, potentiometric
titration, direct measurement using a pH meter, and the like.
Typically, the pH of the at least one polyol is from about 1 to
about 14. More typically, the pH of the at least one polyol is from
about 5 to about 12. Even more typically, the pH of the at least
one polyol is from about 7 to about 10.
[0070] The at least one base is any compound that increases the pH
of the reaction mixture in which the at least one base is
dissolved, dispersed, or suspended. Suitable bases include alkali
metal hydroxides, such as, for example, sodium hydroxide, lithium
hydroxide, potassium hydroxide, rubidium hydroxide, cesium
hydroxide, and mixtures thereof. In an embodiment, the at least one
base comprises sodium hydroxide, lithium hydroxide, potassium
hydroxide, or mixtures thereof.
[0071] The amount of the at least one base is typically from about
5.39.times.10.sup.-5 to about 3.47.times.10.sup.-4 pbw of the at
least one base per 1 pbw of the total amount of the at least one
polyol used in the reaction. More typically, the amount of the at
least one base is typically from about 5.39.times.10.sup.-5 to
about 1.30.times.10.sup.-4 pbw of the at least one base per 1 pbw
of the total amount of the at least one polyol used in the
reaction.
[0072] The total amount of silver compound added to the reaction
mixture over the entire course of the reaction, based on one liter
of reaction mixture, is typically from about 1.5.times.10.sup.-3
mole to about 1 mole of the silver compound (corresponding, in the
case of AgNO.sub.3 as the silver compound and ethylene glycol as
the polyol, to about 0.026 wt % to about 17 wt % AgNO.sub.3 in
ethylene glycol), more typically from greater than or equal to
3.times.10.sup.-2 mole to about 1 mole of the silver compound
(corresponding, in the case of AgNO.sub.3 as the silver compound
and ethylene glycol as the polyol, to about 0.51 wt % to about 17
wt % AgNO.sub.3 in ethylene glycol). The silver compound may be
introduced to the reaction mixture as a solid powder, the total
amount of which may be introduced at one time or which may
introduced in a series of portion of the total amount.
Alternatively, the silver compound may be fed to the reaction
mixture as a dilute solution of the silver compound in the polyol
comprising from about 10 g to about 100 g of the silver compound
per 1000 g polyol at a rate that is sufficiently slow as to avoid
reducing the temperature of the reaction mixture.
[0073] In one embodiment, the total amount of silver compound added
to the reaction mixture is, based on one Liter of reaction mixture,
typically from about 0.02 moles to about 0.22 moles (corresponding,
in the case of AgNO.sub.3 as the silver compound and ethylene
glycol as the polyol, to from about 0.3 wt % to about 3.75 wt %
AgNO.sub.3 in ethylene glycol), more typically from about 0.06
moles to about 0.18 moles (corresponding, in the case of AgNO.sub.3
as the silver compound and ethylene glycol as the polyol, to from
about 1 wt % to 3 wt % AgNO.sub.3 in ethylene glycol), even more
typically from about 0.07 moles to about 0.18 moles (corresponding,
in the case of AgNO.sub.3 as the silver compound and ethylene
glycol as the polyol, to from about 1.25 wt % to about 3 wt %
AgNO.sub.3 in ethylene glycol). In one embodiment, the total amount
of silver compound added to the reaction mixture is, based on one
Liter of reaction mixture, from greater than 0.1 moles to about
0.22 moles (corresponding, in the case of AgNO.sub.3 as the silver
compound and ethylene glycol as the polyol, to from about 1.7 wt %
to about 3.75 wt % AgNO.sub.3 in ethylene glycol).
[0074] In one embodiment, the nanostructures are made in the
presence of from about 5.4.times.10.sup.-5 moles to about
5.4.times.10.sup.-3 moles of particles of silver chloride and/or
particles of silver bromide per Liter of reaction mixture. While
not wishing to be bound by theory, it is believed that the
particles of silver chloride and/or particles of silver bromide
catalyze growth of the silver nanostructures, but do not
participate as a reactive "seeds" that become incorporated within
the silver nanostructures.
[0075] In one embodiment, the at least one polyol and at least one
silver compound are reacted at a temperature of from about
100.degree. C. to about 210.degree. C., more typically from about
130 to about 185.degree. C.
[0076] In one embodiment, at least a portion of the polyol is
preheated to a temperature of from about 100.degree. C. to about
210.degree. C., more typically from about 130.degree. C. to about
185.degree. C., typically for a period of greater than about 1
minute, more typically for a period of greater than about 5 minutes
prior to introduction of the source of chloride or bromide ions,
and/or the silver compound.
[0077] In one embodiment, particles of silver chloride or silver
bromide are formed in the polyol in a preliminary step, wherein a
silver compound and polyol are reacted in the presence of a source
of chloride or bromide ions, typically in with the silver compound
in an excess of from greater than 1, more typically from about 1.01
to about 1.2 moles, of silver compound per mole chloride or bromide
ions. In one embodiment, from about 5.4.times.10.sup.-5 to about
5.4.times.10.sup.-4 moles silver compound per liter of reaction
mixture are reacted in the presence of from about
5.4.times.10.sup.-5 to about 5.4.times.10.sup.-4 moles of the
source of chloride and/or bromide ions per liter of reaction
mixture to form silver chloride and/or silver bromide seed
particles in the reaction mixture. In one embodiment particles of
silver chloride or silver bromide are formed at a temperature of
from about 100.degree. C. to about 210.degree. C., more typically
from about 130.degree. C. to about 185.degree. C. The formation of
the silver chloride or silver bromide particles is typically
conducted over a time period of greater than or equal to about 1
minute, more typically of from about 1 minute to about 10
minutes.
[0078] In one embodiment from about 1.5.times.10.sup.-3 to about 1
mole of the silver compound per Liter of reaction mixture are added
in a second reaction step. The growth step is conducted at a
temperature of about 100.degree. C. to about 210.degree. C., more
typically from about 130.degree. C. to about 185.degree. C. The
second reaction step of the reaction is typically conducted over a
time period of greater than or equal to about 5 minutes, more
typically from about 5 minutes to about 4 hours, and even more
typically from about 10 minutes to 1 about hour.
[0079] In one embodiment, particles of silver chloride or silver
bromide are formed in the polyol simultaneously with the formation
of the silver nanostructures in a single step, wherein a silver
compound and polyol are reacted in the presence of a source of
chloride or bromide ions, typically in with the silver compound in
very large molar excess. The single step formation reaction is
conducted at a temperature of from about 100.degree. C. to about
210.degree. C., more typically from about 130.degree. C. to about
185.degree. C. The single step formation reaction is typically
conducted over a time period of greater than or equal to about 5
minutes, more typically from about 5 minutes to about 4 hours, and
even more typically from about 10 minutes to about 1 hour.
[0080] The reaction may be conducted under an air atmosphere or
under an inert atmosphere, such as a nitrogen or argon atmosphere.
In one embodiment, the reaction is conducted under a nitrogen
atmosphere.
[0081] The copolymer is believed to function as an organic
protective agent. The amount of copolymer is typically from about
0.1 to about 20 parts by weight ("pbw"), more typically from about
1 to about 5 pbw, of the copolymer per 1 pbw of silver compound,
based on the total amount of the silver compound added to the
reaction mixture.
[0082] In one embodiment, the reaction is conducted in the presence
of, based on the weight of the reaction mixture, from about 0.01 wt
% to about 50 wt %, more typically from about 0.1 wt % to about 20
wt %, and even more typically from about 0.5 wt % to 8 wt %, of the
copolymer.
[0083] In one embodiment, the at least one silver compound
comprises silver nitrate, the at least one polyol comprises
ethylene glycol, the total amount of silver nitrate added to the
reaction mixture is from 1.5.times.10.sup.-3 mole to about 1 mole
silver nitrate per Liter of reaction mixture, and the reaction is
conducted in the presence of, based on the weight of the reaction
mixture, from about 0.01 wt % to about 50 wt %, more typically from
about 0.1 wt % to about 20 wt %, and even more typically from about
0.5 wt % to 8 wt %, of the copolymer.
[0084] Saturated or unsaturated five-, six-, or seven-membered
acylamino- or diacylamino-containing heterocylic ring moieties
suitable as the at least one pendant group of the first
constitutional repeating unit of the copolymer include, for
example, pyrrolidonyl, pyrrolidinedionyl, azacyclohexanoyl,
azacyclohexadionyl, azacycloheptanonyl, and
azacycloheptadionyl.
[0085] In one embodiment, the first constitutional repeating units
of the copolymer each independently comprise a pyrrolidonyl moiety
or a pyrrolidinedionyl moiety. In one embodiment, each of the first
constitutive units of the copolymer comprises a pyrrolidonyl
moiety.
[0086] In one embodiment, the first constitutional repeating units
each independently comprise a pendant group according to structure
(I):
R.sup.1--R.sup.2-- (I)
wherein: [0087] R.sup.1 is a saturated or unsaturated five-, six-,
or seven-membered acylamino- or diacylamino-containing heterocylic
ring moiety, more typically pyrrolidonyl, 2,5 pyrrolidinedionyl,
azacyclohexanonyl, azacyclohexadionyl azacycloheptanonyl,
azacycloheptadionyl, even more typically pyrrolidonyl or 2,5
pyrrolidinedionyl, and [0088] R.sup.2 is divalent linking group,
more typically a divalent linking group selected from
poly(alkyleneoxy), --O--C(O)--, --NH--C(O)-- and
--(CH.sub.2).sub.n--, wherein n is an integer of from 1 to 10, more
typically of from 1 to 3, or is absent.
[0089] The first constitutional repeating units may be made by
known synthetic techniques, such as, for example, by grafting of
one or more five-, six-, or seven-membered saturated or unsaturated
acylamino- or diacylamino-containing heterocylic ring moieties onto
a polymer backbone, such as a hydrocarbon polymer backbone, a
polyester polymer backbone, or a polysaccharide polymer backbone,
or by copolymerization of a nonionic monomer, as described below,
with, for example, an ionic monomer, as described below.
[0090] In one embodiment, the first constitutional repeating units
of the copolymer of the present invention are derived from a first
monomer comprising at least one reactive functional group and at
least one five-, six-, or seven-membered saturated or unsaturated
acylamino- or diacylamino-containing heterocylic ring moiety per
molecule of the monomer.
[0091] Suitable reactive functional groups include, for example,
hydroxyl groups, isocyanate groups, epoxide groups, amino groups,
carboxylate groups, and .alpha.,.beta.-unsaturated groups, such as
--CH.sub.2.dbd.CH.sub.2, or --H(CH.sub.3)C.dbd.CH.sub.2.
[0092] In one embodiment, the first monomer comprises one or more
compounds according to structure (II):
R.sup.1--R.sup.2--R.sup.3 (II)
wherein: [0093] R.sup.1 and R.sup.2 are as described above, and
[0094] R.sup.3 is a reactive functional group, more typically a
reactive group selected from --CH.sub.2.dbd.CH.sub.2, and
--H(CH.sub.3)C.dbd.CH.sub.2.
[0095] In one embodiment, the first constitutional repeating units
of the copolymer of the present invention are derived from a first
monomer selected from vinyl pyrrolidone. vinyl caprolactam, and
mixtures thereof. More typically, each of the first constitutional
repeating units of the copolymer of the present invention is
derived from vinylpyrrolidone.
[0096] Constitutional repeating units suitable as the second
constitutional repeating units of the copolymer of the present
invention may be any constitutional repeating units that differ in
composition from the first constitutional repeating units.
[0097] In one embodiment, the second constitutional repeating units
each comprise at least one pendant moiety per second constitutional
repeating unit that: (i) is selected from ionic organic moieties
and nonionic organic moieties, and (ii) is not a saturated or
unsaturated, five-, six-, or seven-membered, acylamino- or
diacylamino-containing heterocylic ring moiety.
[0098] In one embodiment, the second constitutional repeating units
each comprise at least one pendant moiety per second constitutional
repeating unit that is selected from ionic organic moieties.
Suitable ionic organic moieties include cationic moieties, anionic
moieties, and amphoteric/zwitterionic moieties.
[0099] In one embodiment, one or more of the second constitutional
repeating units comprise at least one pendant cationic moiety.
[0100] Suitable cationic moieties include nitrogenous organic
moieties that comprise a primary, secondary, or tertiary amino
nitrogen atom, or a quaternary nitrogen atom. In those embodiments
comprising a quaternary nitrogen atom, the, the cationic moiety is
typically in the form of a salt that is associated with a counter
anion, which may be selected from organic anions, such as
sulphonate anions, and inorganic anions, such as halogen anions or
nitrate anions. In one embodiment, one or more of the second
constitutional repeating units each comprise at least one pendant
cationic moiety that comprises a quaternary ammonium nitrogen atom
and counter anion, more typically a chloride, bromide, or nitrate
counter anion, or a mixture thereof.
[0101] In one embodiment, one or more of the second constitutional
repeating units each independently comprise, per second
constitutional repeating unit, selected from:
[0102] acyclic groups that comprise at least one primary,
secondary, or tertiary amino nitrogen atom or quaternary nitrogen
atom per group, and
[0103] five or six-membered heterocylic ring-containing groups that
comprise at least one nitrogen atom, which may be a quaternary
nitrogen atom, as a ring member.
[0104] Five or six-membered heterocylic ring-containing groups
suitable as the at least one nitrogenous cationic group of the
second constitutive unit, include, for example, pyrrolidinyl,
pyrrolinyl, imidazolidinyl, pyrrolyl, imidazolyl, pyrazolidinyl,
pyrazolinyl, piperidinyl, piperazinyl, pyridinyl, pyrazinyl,
pyrimadinyl, or pyridazinyl groups, more typically quaternized
pyrrolidinyl, quaternized pyrrolinyl, quaternized imidazolidinyl,
quaternized pyrrolyl, quaternized imidazolyl, quaternized
pyrazolidinyl, quaternized pyrazolinyl, quaternized piperidinyl,
quaternized piperazinyl, quaternized pyridinyl, quaternized
pyrazinyl, quaternized pyrimadinyl, or quaternized pyridazinyl
groups.
[0105] In one embodiment, one or more of the second constitutional
repeating units comprise at least one pendant anionic organic
moiety. Suitable anionic moieties include, for example,
carboxylate, sulphonate, sulfate, phosphate, and phosphonate
moieties, such as, for example, alkyl carboxylate moieties, alkyl
sulphonate moieties, alkaryl sulphonate moieties, and alkyl sulfate
moieties, and salts thereof. In some embodiments, the anionic
moiety is in the form of a salt that is associated with a counter
cation, which may be an inorganic cation or an organic cation, such
as an ammonium cation, a cation comprising a primary, secondary, or
tertiary amino nitrogen, a cation comprising a quaternary nitrogen
atom, an alkali metal cation, or a mixture thereof.
[0106] In one embodiment, one or more of the second constitutional
repeating units comprise at least one pendant
amphoteric/zwitterionic organic moiety. Suitable
amphoteric/zwitterionic organic moieties include, for example,
moieties that comprise both a cationic group, such as a quaternary
nitrogen atom, and anionic group, such as a sulphonate group or a
carboxylate group, each of which may independently be in the form
of a salt associated with an oppositely charged counterion, as part
of the same moiety, such as, for example, sulfobetaine moieties or
carboxybetaine moieties.
[0107] In one embodiment, one or more of the second constitutional
repeating units each independently comprise at least one pendant
nonionic organic moiety. Suitable nonionic moieties include
hydrocarbyl moieties, such as alkyl, cycloalkyl, aryl, alkaryl, and
aralkyl moieties, hydroxyalkyl moieties, and poly(alkylene oxide)
moieties.
[0108] In one embodiment, the ionic moiety of the ionic
constitutional repeating units each independently comprise an
acyclic group that comprises at least one quaternized nitrogen
atom, such as a moiety according to formula (III):
R.sup.20--R.sup.21 (III)
wherein: [0109] R.sup.20 is an ionic organic moiety or a nonionic
organic moiety that is not a saturated or unsaturated, five-, six-,
or seven-membered, acylamino- or diacylamino-containing heterocylic
ring moiety, and [0110] R.sup.21 is divalent linking group, more
typically a divalent linking group selected from poly(alkyleneoxy),
--O--C(O)--, --NH--C(O)-- and --(CH.sup.2).sub.m--, wherein m is an
integer of from 1 to 10, more typically of from 1 to 3, or is
absent.
[0111] In one embodiment, the copolymer comprises one or more
second constitutional repeating units that comprise at least one
cationic moiety per such unit. In one embodiment, the copolymer
comprises one or more second constitutional repeating units that
each independently comprise at least one anionic moiety per such
unit. In one embodiment, the copolymer comprises one or more second
constitutional repeating units that each independently comprise at
least one amphoteric/zwitterionic moiety per such unit. In one
embodiment, the copolymer comprises one or more second
constitutional repeating units that each independently comprise at
least one nonionic moiety per such unit. In one embodiment, the
copolymer comprises one or more second constitutional repeating
units that each independently comprise at least one cationic moiety
per such unit and one or more second constitutional repeating units
that each independently comprise at least one anionic moiety per
such unit. In one embodiment, the copolymer comprises one or more
second constitutional repeating units that each independently
comprise at least one cationic moiety per such unit and one or more
second constitutional repeating units that each independently
comprise at least one amphoteric/zwitterionic moiety per such unit.
In one embodiment, the copolymer comprises one or more second
constitutional repeating units that each independently comprise at
least one cationic moiety per such unit and one or more second
constitutional repeating units that each independently comprise at
least one nonionic moiety per such unit. In one embodiment, the
copolymer comprises one or more second constitutional repeating
units that each independently comprise at least one anionic moiety
per such unit and one or more second constitutional repeating units
that each independently comprise at least one
amphoteric/zwitterionic moiety per such unit. In one embodiment,
the copolymer comprises one or more second constitutional repeating
units that each independently comprise at least one anionic moiety
per such unit and one or more second constitutional repeating units
that each independently comprise at least one nonionic moiety per
such unit. In one embodiment, the copolymer comprises one or more
second constitutional repeating units that each independently
comprise at least one amphoteric/zwitterionic moiety per such unit
and one or more second constitutional repeating units that each
independently comprise at least one nonionic moiety per such
unit.
[0112] The second constitutional repeating units may be made by
known synthetic techniques, such as, for example, by grafting of
ionic or nonionic organic moieties onto a polymer backbone, such as
a hydrocarbon polymer backbone, a polyester polymer backbone, or a
polysaccharide polymer backbone, or by copolymerization of a second
monomer, as described below, with, for example, the above-described
first monomer.
[0113] In one embodiment, the second constitutional repeating units
of the copolymer of the present invention are derived from a second
monomer that is copolymerizable with the first monomer and
comprises, per molecule of the monomer, at least one reactive
functional group and at least one nitrogenous cationic group
selected from:
[0114] acyclic groups that comprise at least one primary,
secondary, or tertiary amino nitrogen atom or quaternary nitrogen
atom per group, and
[0115] five or six-membered heterocylic ring-containing groups that
comprise at least one nitrogen atom, which may be a quaternary
nitrogen atom, as a ring member, such as, for example,
pyrrolidinyl, pyrrolinyl, imidazolidinyl, pyrrolyl, imidazolyl,
pyrazolidinyl, pyrazolinyl, piperidinyl, piperazinyl, pyridinyl,
pyrazinyl, pyrimadinyl, or pyridazinyl moiety.
[0116] In one embodiment, the acyclic groups that comprise at least
one primary, secondary, or tertiary amino nitrogen atom or
quaternary nitrogen atom per group is a an acyclic moiety that is
cyclizable, either simultaneously with or subsequent to
copolymerization with the first monomer, to form a five or
six-membered heterocylic ring that comprises at least one nitrogen
atom, which may be a quaternary nitrogen atom, as a ring
member.
[0117] In one embodiment, the second constitutional repeating units
of the copolymer of the present invention are derived from a second
monomer comprising, per molecule of the monomer, at least one
reactive functional group and at least one group that is (i)
selected from ionic organic moieties and nonionic organic moieties,
and (ii) is not a saturated or unsaturated, five-, six-, or
seven-membered, acylamino- or diacylamino-containing heterocylic
ring moiety.
[0118] Suitable reactive functional groups are those described
above in regard to the first monomer.
[0119] In one embodiment, the first monomer comprises one or more
compounds according to structure (IV):
R.sup.20--R.sup.21--R.sup.22 (IV)
[0120] wherein: [0121] R.sup.20 and R.sup.21 are each as described
above, and [0122] R.sup.22 is a reactive functional group, more
typically a reactive group selected from --CH.sub.2.dbd.CH.sub.2,
and --H(CH.sub.3)C.dbd.CH.sub.2.
[0123] Suitable cationic monomers include, for example,
dimethylaminomethyl (meth)acrylate, dimethylaminopropyl
(meth)acrylate, di(t-butyl)aminoethyl (meth)acrylate,
dimethylaminomethyl (meth)acrylamide, dimethylaminoethyl
(meth)acrylamide, dimethylaminopropyl (meth)acrylamide, vinylamine,
vinyl imidazole, vinylpyridine, vinylpyrrolidine, vinylpyrroline,
vinylpyrazolidine, vinylpyrazoline, vinylpiperidine,
vinylpiperazine, vinylpyridine, vinylpyrazine, vinylpyrimadine,
vinylpyridazine, trimethylammonium ethyl (meth)acrylate salts,
dimethylammonium ethyl (meth)acrylate salts, dimethylbenzylammonium
(meth)acrylate salts, benzoylbenzyl dimethylammonium
ethyl(meth)acrylate salts, trimethyl ammonium ethyl
(meth)acrylamido salts, trimethyl ammonium propyl (meth)acrylamido
salts, vinylbenzyl trimethyl ammonium salts, diallyldimethyl
ammonium salts.
[0124] In one embodiment, the second constitutional repeating units
of the copolymer of the present invention are derived from a
cationic monomer selected from diallyldimethylammonium salts, such
as diallyldimethylammonium nitrate, quaternized
dimethylaminoethyl(meth)acrylate salts, such as quaternized
dimethylaminoethyl(meth)acrylate nitrate, and quaternized
vinylimidazole salts, such as quaternized vinylimidazole
nitrate.
[0125] Suitable anionic monomers include, for example, acrylic
acid, acrylic acid, methacrylic acid, vinyl sulphonic acid,
vinylbenzene sulphonic acid, (meth)acrylamidomethylpropane
sulphonic acid, 2-sulphoethyl methacrylate, and styrenesulfonate,
as well as mixtures of and salts thereof.
[0126] Suitable amphoteric/zwitterionic monomers include, for
example, sulfobetaine (meth)acrylates, sulfobetaine
(meth)acrylamides, sulfobetaine (meth)allyl compounds, sulfobetaine
vinyl compounds, carboxybetaine (meth)acrylates, carboxybetaine
(meth)acrylamides, caboxybetaine (meth)allyl compounds and
carboxybetaine vinyl compounds, such as for example,
N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N-dimethyl ammonium
betaine, N-(3-acrylamidopropyl)-N,N-dimethylammonioacetate, or
N-(3-acryloamidopropyl)-N,N-dimethyl-N-(carboxymethyl)ammonium
bromide.
[0127] Suitable nonionic monomers include, for example,
(meth)acrylamide, esters of an monoethylenically unsaturated
monocarboxylic acids, such as methyl (meth)acrylate, ethyl
(meth)acrylate, n-propyl (meth)acrylate, n-butyl(meth)acrylate,
2-ethyl-hexyl (meth)acrylate, or hydroxyalkyl esters such as
2-hydroxyethyl (meth)acrylate, polyethylene and/or polypropylene
oxide (meth)acrylates (i.e. polyethoxylated and/or polypropoxylated
(meth)acrylic acid), vinyl alcohol, vinyl acetate, vinyl versatate,
vinyl nitriles, acrylonitrile, vinyl aromatic compounds, such as
styrene, and mixtures thereof.
[0128] In one embodiment, the copolymer comprises, based on 1000
constitutional repeating units:
[0129] from 500 to 999, more typically from 800 to 999, even more
typically from 900 to 990, first constitutional repeating units,
and
[0130] from 1 to 500, more typically from 1 to 200, even more
typically from 10 to 100 second constitutional repeating units.
[0131] In one embodiment, the copolymer is made by copolymerizing a
mixture of monomers that comprises more first monomers and one or
more second monomers that each independently comprise at least one
cationic moiety per molecule of such monomer. In one embodiment,
the copolymer is made by copolymerizing a mixture of monomers that
comprises one or more first monomers and one or more second
monomers that each independently comprise at least one anionic
moiety per molecule of such monomer. In one embodiment, the
copolymer is made by copolymerizing a mixture of monomers that
comprises one or more first monomers and one or more second
monomers that each independently comprise at least one
amphoteric/zwitterionic moiety per molecule of such monomer. In one
embodiment, the copolymer is made by copolymerizing a mixture of
monomers that comprises one or more first monomers and one or more
second monomers that each independently comprise at least one
nonionic moiety per molecule of such monomer. In one embodiment,
the copolymer is made by copolymerizing a mixture of monomers that
comprises one or more first monomers, one or more second monomers
that each independently comprise at least one cationic moiety per
molecule of such monomer, and one or more second monomers that each
independently comprise at least one anionic moiety per molecule of
such monomer. In one embodiment, the copolymer is made by
copolymerizing a mixture of monomers that comprises one or more
first monomers, one or more second monomers that each independently
comprise at least one cationic moiety per molecule of such monomer,
and one or more second monomers that each independently comprise at
least one amphoteric/zwitterionic moiety per molecule of such
monomer. In one embodiment, the copolymer is made by copolymerizing
a mixture of monomers that comprises one or more first monomers,
one or more second monomers that each independently comprise at
least one cationic moiety per molecule of such monomer, and one or
more second monomers that each independently comprise at least one
nonionic moiety per molecule of such monomer. In one embodiment,
the copolymer is made by copolymerizing a mixture of monomers that
comprises one or more first monomers, one or more second monomers
that each independently comprise at least one anionic moiety per
molecule of such monomer, and one or more second monomers that each
independently comprise at least one amphoteric/zwitterionic moiety
per molecule of such monomer. In one embodiment, the copolymer is
made by copolymerizing a mixture of monomers that comprises one or
more first monomers, one or more second monomers that each
independently comprise at least one anionic moiety per molecule of
such monomer, and one or more second monomers that each
independently comprise at least one nonionic moiety per molecule of
such monomer. In one embodiment, the copolymer is made by
copolymerizing a mixture of monomers that comprises one or more
first monomers, one or more second monomers that each independently
comprise at least one amphoteric/zwitterionic moiety per molecule
of such monomer, and one or more second monomers that each
independently comprise at least one nonionic moiety per molecule of
such monomer.
[0132] In one embodiment, the copolymer is made by copolymerizing a
mixture of monomers, comprising, based on 1000 moles of such
monomers: [0133] (a) from 800 to 999 moles of one or more first
monomers, each independently comprising at least one reactive
functional group per molecule and at least one pendant saturated or
unsaturated, five-, six-, or seven-membered acylamino- or
diacylamino-containing heterocylic ring moiety per molecule, and
[0134] (b) from 1 to 200 moles of one or more second monomers, each
independently comprising at least one reactive functional group per
molecule and at least one pendant organic moiety that comprises at
least one primary, secondary, or tertiary amino nitrogen atom or
quaternary nitrogen atom per molecule.
[0135] The copolymer of the present invention typically has weight
average molecular weight of greater than or equal to 5,000 grams
per mole (g/mol), more typically, a weight average molecular weight
of from about 10,000 to about 2,000,000 g/mol, even more typically
from about 10,000 to about 500,000 g/mol, and still more typically
from about 10,000 to about 100,000 g/mol.
[0136] In one embodiment, the copolymer is a random copolymer,
comprising chains of randomly arranged first constitutional
repeating units and second constitutional repeating units. In one
embodiment, the copolymer is a block copolymer, comprising blocks
of two or more consecutive first constitutional repeating units and
blocks of two or more consecutive second constitutive units.
[0137] Methods for making suitable copolymers are known in the art.
In one embodiment, the polymer according to the present invention
is made by copolymerization of ethylenically unsaturated monomers
according to known free radical polymerization processes. In one
embodiment, the copolymer is made by a controlled free radical
polymerization techniques, such as the known controlled free
radical polymerization processes of atom transfer radical
polymerization ("ATRP"), reversible addition fragmentation transfer
("RAFT" polymerization), or macromolecular design via interchange
of xanthates ("MADIX" polymerization).
[0138] If the second monomer comprises a reactive group that is
cyclizable to form a five or six-membered heterocylic ring that
comprises at least one quaternized or quaternizable nitrogen atom
as a ring member, the cyclization to form the heterocylic ring
structure may be conducted simultaneously with the copolymerization
with the first monomer, such as by, for example, simultaneous
polymerization and cyclization of a quaternized or quaternizable
nitrogen atom-containing diallyl monomer, or conducted subsequent
to such polymerization.
[0139] If the second monomer comprises a quaternizable nitrogen
atom as a ring member, then the nitrogen may be quaternized
subsequent to the polymerization reaction.
[0140] In one embodiment, the copolymer is a random copolymer made
by free radical polymerization of vinyl pyrrolidone, vinyl
caprolactam, or vinyl pyrrolidone and vinyl caprolactam with one or
more ethylenically unsaturated cationic monomers.
[0141] In one embodiment, the copolymer is a random copolymer made
by free radical polymerization of a monomer mixture comprising from
about 80 pbw to less than 100 pbw, more typically from about 90 pbw
to about 99 pbw, of vinyl pyrrolidone and from greater than 0 to
about 20 pbw, more typically from about 1 to about 10 pbw, of a
diallyldimethylammonium salt.
[0142] In one embodiment, the at least one silver compound
comprises silver nitrate, the at least one polyol comprises
ethylene glycol, the total amount of silver nitrate added to the
reaction mixture is from 1.5.times.10.sup.-3 mole to about 1 mole
silver nitrate per Liter of reaction mixture, the reaction is
conducted in the presence of, based on the weight of the reaction
mixture, from about 0.01 wt % to about 50 wt %, more typically from
about 0.1 wt % to about 20 wt %, and even more typically from about
0.5 wt % to 8 wt %, of a random copolymer made by free radical
polymerization of a monomer mixture comprising from about 80 pbw to
less than 100 pbw, more typically from about 90 pbw to about 99
pbw, of vinyl pyrrolidone and from greater than 0 to about 20 pbw,
more typically from about 1 to about 10 pbw, of a
diallyldimethylammonium salt.
[0143] The process of the present invention typically produces a
high yield of silver nanowires. In one embodiment, greater than or
equal to 70 wt % of silver feed is converted to nanowires and less
than 30 wt % of silver feed is converted to isotropic
nanostructures, more typically greater than or equal to 80 wt % of
silver feed is converted to nanowires and less than 20 wt % of
silver feed is converted to isotropic nanoparticles, and even more
typically more than 90 wt % of silver feed is converted to
nanowires and less than 10 wt % of silver feed is converted to
isotropic nanostructures. In one embodiment, greater than or equal
to 99 wt % of silver feed is converted to nanowires and less than 1
wt % of silver feed is converted to isotropic nanostructures.
[0144] In one embodiment, the silver nanostructures comprise
elongated silver nanostructures, known as "silver nanowires" having
a diameter of from about 10 nm to about 2 .mu.m, more typically
from about 10 nm to about 150 nm, even more typically from about 10
nm to about 60 nm, and a length of from about 5 .mu.m to about 300
.mu.m, more typically from about 10 to about 200 .mu.m.
[0145] In one embodiment, the silver nanostructures comprise silver
nanowires having a diameter of from about 10 nm to about 150 nm,
even more typically from about 10 nm to about 60 nm, and an aspect
ratio, that is, a length to diameter ratio, of greater than 100, or
greater than 150, or greater than 200, or greater than 300.
[0146] In one embodiment, the nanowires made by the process of the
present invention exhibit an aspect ratio that is, on average,
greater than that of nanowires made by an analogous product wherein
poly(vinyl pyrrolidone) is substituted for the copolymer component
of the process of the present invention. In one embodiment, the
nanowires made by the process of the present invention exhibit an
aspect ratio that is, on average, greater than that of nanowires
made by an analogous product wherein poly(vinyl pyrrolidone is
substituted for the copolymer component of the process of the
present invention by a factor of a least 2, more typically by a
factor of at least 3.
[0147] The product mixture comprises polyol, copolymer, and silver
nanostructures, wherein the silver nanostructures comprise silver
nanowires and may comprise silver nanostructures other than silver
nanowires, such as, isotropic silver particles.
[0148] The silver nanostructures may be isolated from the polyol
and copolymer components of the product mixture by, for example,
gravity separation, centrifugation, or filtration. In one
embodiment, the silver nanostructures are then washed in water, an
alcohol, typically a (C.sub.1-C.sub.3)alkanol, or a mixture of
water and alkanol, to remove residues of the polyol and copolymer
from the isolated nanowires.
[0149] Silver nanowires produced by the process of the present
invention may be separated from other non-nanowire silver
nanostructure components that may be present in the product mixture
by dispersing the silver nanostructures in a polar aprotic organic
liquid, such as acetone or acetonitrile, followed by isolation of
the nanowires from the liquid by gravity separation or
centrifugation. The silver nanowires tend to agglomerate and
precipitate from the polar aprotic liquid, while isotropic silver
nanostructures tend to remain suspended in the polar aprotic
organic liquid.
[0150] In one embodiment, the product mixture is subjected to
gravity separation, the silver nanowire fraction of the separated
product mixture is re-dispersed in acetone and subjected to gravity
separation and the silver nanowire fraction of the separated
acetone dispersion is the re-dispersed in water, alcohol or a
mixture thereof.
[0151] The residue of the copolymer used in the process of the
present invention is more easily cleaned from the silver
nanostructure product than the poly(vinylpyrrolidone) homopolymer
of prior art processes, which typically require multiple iterations
of water or water and alcohol washing to remove from the silver
nanostructure product. For example, the copolymer residue may
typically be removed from the silver nanostructures in a single
water/alkanol washing step, while removal of poly(vinyl pyrrolidone
homopolymer residue from silver nanostructures typically requires
form 5 to 10 iterations of an analogous water/alkanol washing step.
Reducing the amount of or eliminating the copolymer or homopolymer
from the dispersion of silver nanowires is of great benefit in
using the silver nanowires to easily make electrically conductive
polymer films having very high conductivity. The silver nanowires
of the dispersion of the present invention can be used to make
polymer films having high electrical conductivity without requiring
the extra steps required by prior art processes, such as iterative
washing steps or heat treating or heating and compressing the
silver nanowire network to displace a coating of vinylpyrrolidone
residue from the surfaces of the nanowires and allow metal to metal
contact between the nanowires of the network.
[0152] In one embodiment, silver nanowires are provided in the form
of a dispersion comprising silver nanowires dispersed in liquid
medium comprising water, a (C.sub.1-C.sub.6)alkanol, or a mixture
thereof. Including an alkanol component in the liquid medium of the
dispersion is of benefit in reducing oxidation of the silver
nanostructure component of the dispersion.
[0153] In one embodiment, the nanowire dispersion comprises silver
nanowires dispersed in aqueous medium wherein the dispersion
comprises less than 100 pbw, or less than 10 pbw, or less than 5
pbw or less than 1 pbw of the copolymer per 1,000,000 pbw of silver
nanowires. In one embodiment, the dispersion comprises no
detectable amount of the copolymer.
[0154] The silver nanowires made by the process of the present
invention are useful in combination with an electrically conductive
polymer, as a component of an electrically conductive film.
Suitable electrically conductive polymers include electrically
conductive polythiophene polymers, electrically conductive
poly(selenophene)polymers, electrically conductive
poly(telurophene) polymers, electrically conductive polypyrrole
polymers, electrically conductive polyaniline polymers,
electrically conductive fused polycylic heteroaromatic polymers,
and blends of any such polymers. In one embodiment, the
electrically conductive polymer comprises a doped electrically
conductive polymer known as PEDT:PSS, which comprises
poly(3,4-ethylenedioxythiophene or "PEDOT" and a water soluble
polymeric acid dopant comprising a poly(styrene sulfonic acid) or
"PSS". Such electrically conductive polymer films typically exhibit
high conductivity and high optical transparency and are useful as a
layer in an electronic device. Suitable electronic devices include
any device that comprises one or more layers of semiconductor
materials and makes use of the controlled motion of electrons
through such one or more layers, such as, for example: devices that
converts electrical energy into radiation, such as, for example,
light-emitting diodes, light emitting diode displays, diode lasers,
or lighting panels, devices that detect signals through electronic
processes, such as, for example, photodetectors, photoconductive
cells, photoresistors, photoswitchs, phototransistors, phototubes,
infrared ("IR") detectors, or biosensors, devices that convert
radiation into electrical energy, such as, for example,
photovoltaic devices or solar cells, and devices that includes one
or more electronic components with one or more semiconductor
layers, such as, for example, transistors or diodes.
[0155] In one embodiment, the process of the present invention
permits the use of a higher concentration of silver compound, for
example silver nitrate, in the reaction mixture which enables
production of a product mixture having a higher concentration of
silver nanostructures, more typically silver nanowires, than an
analogous process wherein poly(vinyl(pyrrolidone) homopolymer is
used in place of the copolymer component of the process of the
present invention.
[0156] In one embodiment, the process of the present invention
enables production of silver nanowires having a higher aspect ratio
than silver nanowires made by an analogous process wherein
poly(vinyl(pyrrolidone) homopolymer is used in place of the
copolymer component of the process of the present invention.
[0157] In general, silver nanostructures made by the process of the
present invention are more easily cleaned than silver
nanostructures made by an analogous process wherein
poly(vinyl(pyrrolidone) homopolymer is used in place of the
copolymer component of the process of the present invention,
because residues of the copolymer component of the process of the
present invention is more easily removed from silver nanowires
structures than are residues of poly(vinyl pyrrolidone)
homopolymer.
Examples 1A-1E and Comparative Example C1
[0158] The poly(vinylpyrrolidone-co-diallyldimethylammonium
nitrate) random copolymers ("poly(VP-co-DADMAN") of Examples 1A-1E
were each made by copolymerizing vinylpyrrolidone monomer with
diallyldimethylammonium nitrate monomer ("DADMAN").
[0159] DADMAN monomer was made by exchanging the chloride counter
ion of diallyldimethylammonium chloride monomer ("DADMAC", shown in
structure (b) above) with nitrate counter ions, using silver
nitrate, according to reaction:
[0160]
C.sub.8h.sub.16N.sup.+Cl.sup.-+AgNO.sub.3.fwdarw.AgCl+C.sub.8H.sub.-
16N.sup.+NO.sub.3.sup.-. The exchange of chloride for nitrate ions
was done by adding the adequate amount of a solution of silver
nitrate in water (1:1 molar ratio between Cl.sup.- and NO.sub.3)
into X/0.6 g of a solution of 60 wt % DADMAC in water, where X=1,
2, 4, 8, or 16.
[0161] The exchanges each occurred quickly and produced a white
silver chloride precipitate that was easily separated from the
DAMAN monomer product solutions by centrifugation (5 min at 2000
rpm). The precipitates were washed one time with 5 ml of water and
centrifuged again in order to retrieve all the monomer. The total
exchanged monomer solutions were then filtered with a 0.2 .mu.m
filter prior to use in copolymerization reactions, as described
below.
[0162] VP and DADMAN monomers were copolymerized according to the
general Scheme A below, using controlled radical polymerization
using azobisisobutyronitrile (AIBN) as the polymerization initiator
and a thiocarbonylthio transfer agent, to produce a linear
poly(VP-co-DADMAN) copolymer.
##STR00001##
[0163] In a 500 ml jacketed reactor, 90 g of vinylpyrrolidone (VP),
0.2 ml of the thiocarbonylthio transfer agent and an aqueous DADMAN
solution were heated to 68.degree. C. under nitrogen. A solution of
0.5 g of AIBN in 10 g of VP was then added stepwise in the
solution, according to the following schedule: [0164] at t=0, 2 ml
of the AIBN/VP solution was added to the solution, [0165] at t=20
min, the temperature had increased to about 75.degree. C., due to
exothermic polymerization reaction, and 0.5 ml of AIBN/VP solution
were added, and [0166] at t=55 min, the temperature in the reactor
was about 78.degree. C., 150 ml of water pre-heated to 68.degree.
C. were added to the reaction mixture with the rest of the AIBN/VP
solution.
[0167] Following addition of the water and final AIBN/VP solution,
the reaction mixture was kept at 68.degree. C. for 4 more hours and
then allowed to cool at room temperature for another 6 to 10 hours.
The viscous product solution so produced was then precipitated in
750 ml of acetone and washed twice with 100 ml aliquots of acetone.
The washed product was then dried at 70.degree. C. under vacuum
with nitrogen purge for one day, and then ground and dried again
before use. The theoretical weight average molecular weight
obtained by above described polymerization process is about 100,000
g/mol. The yield of this process was typically about 75%.
Representative 1H NMR and FTIR spectra of the copolymer product are
shown in FIGS. 1(a) and 1(b).
[0168] The poly(vinyl pyrrolidone) homopolymer of Comparative
Example C1 was made by a process analogous to that used to make the
copolymers of Examples 1A-1E, but using only vinyl pyrrolidone
monomer, that is, no DADMAN monomer was included in the reaction
mixture.
TABLE-US-00001 TABLE I DADMAN Example # content (wt %) C1 0 1A 1 1B
2 1C 4 1D 8 1E 16
Examples 2A-2G and Comparative Examples C2A-C2C
[0169] The silver nanowires of Examples 2A-2G were made according
to the general synthesis process described below, wherein the
composition of the copolymer and the amount of silver nitrate added
to the reaction mixture were varied. In each case, a respective one
of the poly(VP-co-DADMAN) copolymers of Example 1A-1E was used as a
protectant.
[0170] Typically, 35 g of ethylene glycol with 0.0055 g of lithium
chloride were heated to 173.degree. C., with nitrogen purge, for 1
hour. The poly(VP-co-DADMAN) copolymer (typically in an amount of
1.5 g) was added at the end of this pre-treatment. A feed solution
consisting of a given amount (between 0.3 and 1.5 g) of silver
nitrate dissolved in 7.5 g of ethylene glycol was used to introduce
silver nitrate and more ethylene glycol into the reaction mixture.
In a seeding step, an initial amount of silver nitrate (0.05 g,
typically in the form of 0.34 mL of a feed solution containing 1 g
of silver nitrate in 7.5 g of ethylene glycol) was then fed into
the reaction mixture, upon which the reaction mixture turned brown
in color. After 6 minutes, the remainder of the silver nitrate feed
solution was added to the reaction mixture using a syringe, at a
rate of 1.5 ml/min. As the silver nitrate feed was added, the
reaction mixture darkened, turned grey in color, and then,
typically within about 7 minutes after the beginning of the
addition of the silver nitrate feed, nanowires became visible in
the reaction mixture. Depending on the total amount of silver
nitrate added, the reaction took from about 15 to about 30 minutes
reach completion.
[0171] The pH of the ethylene glycol used (high-purity anhydrous
ethylene glycol; Sigma-Aldrich Lot SHBB8374V; "Lot A") in the
reaction mixture was determined to be 8.9 by dilution and
titration. The pH of the pure ethylene glycol can be read on the
vertical axis, for V=0 mL, of the titration curve shown in FIG. 5.
Lot A ethylene glycol was used in the present examples 2A-2G and
Comparative Examples C2A-C2C as well as following Examples 3 and
4.
[0172] The silver nanowires of Comparative Examples C2-A to C2-C
were made by an analogous process to that used to make the silver
nanowires of Examples 2A-2G, except that poly(VP) homopolymer of
Comparative Example C1 was substituted for poly(VP-co-DADMAN)
copolymer.
[0173] For each synthesis, the reaction was left to react until
complete reduction of silver nitrate. The nanowires of Examples
2A-2G were isolated form the reaction mixture by gravity separation
and the poly(VP-co-DADMAN residues were removed from the nanowires
by washing with a mixture of water and alkanol. The nanowires of
Comparative Examples C1-C3 were isolated from the reaction mixture
by gravity separation and removal of the poly(VP) residues from the
nanowires required multiple (at least 5) iterations of the
water/alkanol washing step. In each case, silver nanowires were
separated from isotropic silver nanostructures by agglomerating the
silver nanowires in a mixture of acetone and water and collecting
the agglomerated silver nanowires.
[0174] An optical microscope was used to follow the evolution of
each reaction and to determine the physical characteristics of the
product nanostructures. The polymer or copolymer used in the
nanowire synthesis reaction (and in the case of poly(VP-co-DADMAN)
copolymers, the DADMAN content of the copolymer) and amount of
AgNO.sub.3 used in to make the silver nanowires of Examples 2A-2G
and Comparative Examples C2A-C2C and the numerical average length
of the respective silver nanowires are summarized in TABLE II
below.
TABLE-US-00002 TABLE II Polymer or Copolymer AgNO.sub.3 Nanowire
Nanowire used in synthesis AgNO.sub.3 Amount length Ex# Ex # (wt %)
(g) (.mu.m) 2A 1A (1 wt % DADMAN) 1.25 0.5 15 2B 1A (1 wt % DADMAN)
2.5 1 25 2C 1B (2 wt % DADMAN) 2.5 1 16 2D 1B (2 wt % DADMAN) 2.9
1.16 18 2E 1D (8 wt % DADMAN) 1.25 0.5 5 2F 1D (8 wt % DADMAN) 2.5
1 20 2G 1D (8 wt % DADMAN) 3.75 1.5 27 C2A C1 (poly(VP) 1 0.4 10
homopolymer) C2B C1 (poly(VP) 1.25 0.5 12 homopolymer) C2C C1
(poly(VP) 2.5 1 produced an homopolymer) agglomerate of
unrecoverable nanostructures
[0175] The results are also summarized in FIG. 2 as a plot of
nanowire diameter as a function of the amount of AgNO.sub.3 used in
the nanowire synthesis and amount of DADMAN in the copolymer used
in the nanowire synthesis. The product nanostructures were
classified as "thin nanowires" (nanostructures less than or equal
to 150 nm in diameter and greater than 5 .mu.m in length), "thick
nanowires" (nanostructures greater than 150 nm in diameter and
greater than 5 .mu.m in length) and/or "nanoparticles"
(nanostructures less than or equal to 5 .mu.m in length). The plot
allows the visualization of three regions, that is, a
"Nanoparticles" region, wherein the silver nanostructure product
was predominately nanoparticles and two nanowire regions,
"Nanowires--Zone I", wherein the silver nanostructure product was
predominately thin nanowires, and "Nanowires--Zone II", wherein the
silver nanostructure product was a mixture of thin nanowires and
thick nanowires, with a boundary line "C.sub.thin" between the
Nanoparticles region and Nanowires Zone I, and a boundary line
"C.sub.thick" between Nanowires--Zone I and Nanowires--Zone II.
[0176] The results plotted FIG. 2 indicate that using
poly(VP-co-DADMAN) copolymer instead of poly(VP) homopolymer shifts
production of thin silver nanowires toward higher concentration of
silver nitrate and that synthesis of thin silver nanowires can be
achieved at concentrations up to 3 times higher than in pure
poly(VP) homopolymer and that this effect increases dramatically as
DADMAN content of the poly(VP-co-DADMAN) copolymer increases from 0
to about 2 wt % and continues to increase, although less
dramatically as the DADMAN content further increased from 2 wt % to
8%. Increasing DADMAN content above 8 wt % did not appear to
provide any further significant benefit, in that poly(VP/DADMAN)
copolymer having a DADMAN content of 8 wt % and poly(VP/DADMAN)
copolymer having a DADMAN content of 16% each appeared to give the
substantially same results.
[0177] The diameter of the silver nanowires can be determined by
transmission electron microscopy (TEM) and/or scanning electron
microscopy (SEM). A TEM image of the silver nanowire of Example 2A
is shown in FIG. 6. The diameter of the silver nanowires of Example
2A is 55 nm.
Example 3
[0178] The silver nanostructures of Examples 3A-3C were made
substantially in accord with the process used to make the nanowires
of Examples 2A-2G, as described above, using 0.5 g of the
poly(VP-co-DADMAN) copolymer of Example 1E (16 wt % DADMAN
content), except that the amount of silver nitrate added to the
reaction mixture was varied. The length distribution of the as
produced nanostructures was determined using the image analysis
software "Image)" on picture taken with an optical microscope.
[0179] FIG. 3 shows the size distributions of the nanostructure
products of Examples 3A-3C. The amount of AgNO.sub.3 used in each
synthesis, as well as the symbol used to represent the
nanostructure product in FIG. 3, is listed in TABLE III below.
TABLE-US-00003 TABLE III Example # Symbol In FIG. 3 AgNO.sub.3 (wt
%) AgNO.sub.3, amount (g) 3A square 1.25 0.5 3B X 2.5 1 3C triangle
3.75 1.5
[0180] For AgNO.sub.3 concentrations of 1.25 wt % and 2.5w %, only
thin nanowires were produced, wherein the nanowires produced at 2.5
wt % AgNO.sub.3 were significantly longer (mean length of about 20
.mu.m) than those produced at 1.25 wt % AgNO.sub.3 (mean length of
about 10 .mu.m. At a AgNO.sub.3 concentration of 3.75 wt %, a
mixture of thin nanowires and thick nanowires was produced.
Example 4
[0181] The silver nanowires of Examples 4A and 4 B were made
according the process described above in Examples 2A-2G, using
poly(VP-co-DADMAN) having a1 wt % DAMAN content at two different
amounts of AgNO.sub.3.
[0182] FIG. 4 shows the size distributions of the nanostructure
products Examples 4A and 4B. The amount of AgNO.sub.3 used in each
synthesis, as well as the symbol used to represent the
nanostructure product in FIG. 4, is listed in TABLE IV below.
TABLE-US-00004 TABLE IV Symbol in Zone of AgNO.sub.3 AgNO.sub.3
Example # FIG. 4 FIG. 2 (wt %) amount (g) 4A triangle I 1.25 0.5 4B
X II 2.5 1
Example 5
[0183] Reduced-Water Synthesis of Poly(VP-Co-DADMAN) Having a 1 Wt
% DADMAN Content
[0184] The synthesis of poly(VP-co-DADMAN) is composed of two
steps:
[0185] The first step was a counter-ion exchange to form DADMAN
(Diallydimethylammonium nitrate) from commercially-available DADMAC
(Diallydimethylammonium chloride). To exchange the counter-ion, a
solution of 13.54 g of AgNO.sub.3 dissolved in 6.44 g of deionized
water was added to 21.00 g of DADMAC in water (65 wt %). The molar
ratio of AgNO.sub.3 to DADMAC is 1 to 1.05 in order to remove all
of the AgNO.sub.3 (which would otherwise give a black color to the
solution). After vortex stirring, two phases appeared. The liquid
supernatant, which contained DADMAN in water, is collected. The
white silver solid precipitate of AgCl is washed with 5 mL of water
and then centrifuged a second time to extract all the DADMAN
monomer from it. The combined supernatants were filtered through a
0.20 .mu.m filter and added to 1452 g of vinylpyrrolidone (VP) and
130 g of molecular sieves. The monomers were shaken for an hour
after which the sieves were removed. The solution was subsequently
introduced into a 5-L three-necked round-bottomed flask
reactor.
[0186] Initiator solution was prepared separately by adding 2.20 g
of AIBN to 20.8 g (about 20 mL) of VP.
[0187] The mixture of monomers was heated up to 60.degree. C. and
stirred. 6.66 g of thiocarbonylthio transfer agent and 2.5 g of
initiator solution were added to the 5-L flask. Then, 2.5 g of the
initiator solution was added every 30 minutes. The reaction
temperature was maintained between 57 and 62.degree. C. After 7.5
hours, 500 g of methanol was added to the flask to reduce the
viscosity of the reactant and the reaction was allowed to stir for
up to 12 hours. A yellow viscous transparent liquid was
obtained.
[0188] Since VP and DADMAN are soluble in diethyl ether and
poly(VP-co-DADMAN) is not, the copolymer was isolated from
remaining monomer by selective precipitation in this solvent. Two
volumes of ether were used for 1 volume of copolymer. The ether was
removed from the resulting white precipitate, which was
subsequently dried in a hood and then in a vacuum oven. The dried
copolymer was ground to obtain a white, slightly yellow, fine
powder.
Example 6
[0189] Alternative Reduced-Water Synthesis of Poly(VP-Co-DADMAN)
Having a 1 Wt % DADMAN Content
The synthesis of poly(VP-co-DADMAN) is composed of two steps:
[0190] The first step was a counter-ion exchange to form DADMAN
(Diallydimethylammonium nitrate) from commercially-available DADMAC
(Diallydimethylammonium chloride). To exchange the counter-ion, a
solution of 13.54 g of AgNO.sub.3 dissolved in 6.44 g of deionized
water was added to 21.00 g of DADMAC in water (65 wt %). The molar
ratio of AgNO.sub.3 to DADMAC is 1 to 1.05 in order to remove all
of the AgNO.sub.3 (which would otherwise give a black color to the
solution). After vortex stirring, two phases appeared. The liquid
supernatant, which contained DADMAN in water, is collected. The
white silver solid precipitate of AgCl is washed with 5 mL of water
and then centrifuged a second time to extract all the DADMAN
monomer from it. The combined supernatants were filtered through a
0.20 .mu.m filter and added to 1452 g of vinylpyrrolidone (VP) and
130 g of molecular sieves. The monomers were shaken for an hour
after which the sieves were removed. The solution was subsequently
introduced into a 5-L three-necked round-bottomed flask
reactor.
[0191] Initiator solution was prepared separately by adding 2.20 g
of AIBN to 20.8 g (about 20 mL) of VP.
[0192] The mixture of monomers was heated up to 60.degree. C. and
stirred. 6.66 g of thiocarbonylthio transfer agent and 2.5 g of
initiator solution were added to the 5-L flask. Then, 2.5 g of the
initiator solution was added every 30 minutes. The reaction
temperature was maintained between 57 and 62.degree. C.
[0193] After 7.5 hours, 500 g of ethylene glycol was added to the
flask to reduce the viscosity of the reactant. The temperature was
raised to 70.degree. C., and another 500 g of ethylene glycol was
added after one hour. The reaction was allowed stir for up to 12
hours. A yellow viscous transparent liquid was obtained.
[0194] The copolymer suspension is used as is in silver nanowire
synthesis without further purification.
Example 7
[0195] High aspect ratio silver nanowires were achieved using
poly(VP-co-DADMAN) in ethylene glycol that required the addition of
a base.
[0196] The pH of the ethylene glycol used (high-purity anhydrous
ethylene glycol; Sigma-Aldrich Lot SHBC6651V; "Lot B") in the
reaction mixture was determined to be 4.6 by dilution and
titration. The pH of the pure ethylene glycol can be read on the
vertical axis, for V=0 mL, of the titration curve shown in FIG. 7.
Lot B ethylene glycol was used in the present Example 7 and in the
following Examples 8 and 9.
[0197] mg of lithium chloride (LiCl), 2.4 mg lithium hydroxide
(LiOH), and 0.5 g poly(VP-co-DADMAN) having a 1 wt % DAMAN content
were added to 44 g of ethylene glycol and heated to 175.degree. C.
for 30 minutes under nitrogen atmosphere and moderate agitation
(100-300 rpm). In the seeding step, an initial amount of silver
nitrate (14 mg AgNO.sub.3 dissolved in 0.45 mL ethylene glycol) was
then added into the reaction mixture. A silver nitrate feed
solution (with 0.37 gm of AgNO.sub.3 dissolved in 12 g ethylene
glycol) was then fed dropwise to the reaction mixture at a rate of
1.5 mL/minute. The reaction was stopped after 15 minutes from the
start of the feed by quenching the solution in ice.
[0198] The nanowires of Example 7 were isolated form the reaction
mixture by gravity separation and the poly(VP-co-DADMAN residues
were removed substantially according to the isolation steps
described in the previous Examples.
[0199] An SEM image of the nanowires of Example 7 is shown in FIG.
8. The average diameter of the nanowires was found to be about 47
nm, and the average length was found to be about 20 .mu.m. FIG. 9
shows an image of the nanowires of Example 7 as seen through
optical microscopy.
Example 8
[0200] The silver nanowires of Example 8 were made by an analogous
process to that used to make the silver nanowires of Example 7,
except that LiOH was replaced with 5.8 mg of potassium hydroxide
(KOH).
[0201] FIG. 10 shows an image of the nanowires of Example 8 as seen
through optical microscopy. The average diameter of the nanowires
of Example 8 was found to be about 65 nm, and the average length
was found to be about 25 .mu.m.
Example 9
[0202] The silver nanowires of Example 9 were made by an analogous
process to that used to make the silver nanowires of Example 7,
except that LiOH was replaced with 4.1 mg of sodium hydroxide
(NaOH).
[0203] FIG. 11 shows an image of the nanowires of Example 9 as seen
through optical microscopy. The average diameter of the nanowires
of Example 9 was found to be about 57 nm, and the average length
was found to be about 22 .mu.m.
* * * * *