U.S. patent application number 16/457816 was filed with the patent office on 2019-12-12 for highly tunable magnetic liquid crystals.
The applicant listed for this patent is The Regents of the University of California. Invention is credited to Mingsheng Wang, Yadong Yin.
Application Number | 20190377215 16/457816 |
Document ID | / |
Family ID | 54288297 |
Filed Date | 2019-12-12 |
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United States Patent
Application |
20190377215 |
Kind Code |
A1 |
Yin; Yadong ; et
al. |
December 12, 2019 |
HIGHLY TUNABLE MAGNETIC LIQUID CRYSTALS
Abstract
In various embodiments magnetically actuated liquid crystals are
provided as well as method of manufacturing such, methods of using
the liquid crystals and devices incorporating the liquid crystals.
In one non-limiting embodiment the liquid crystals comprise
Fe.sub.3O.sub.4 nanorods where the nanorods are coated with a
silica coating.
Inventors: |
Yin; Yadong; (Riverside,
CA) ; Wang; Mingsheng; (Lake Forest, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
The Regents of the University of California |
Oakland |
CA |
US |
|
|
Family ID: |
54288297 |
Appl. No.: |
16/457816 |
Filed: |
June 28, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15301699 |
Oct 3, 2016 |
10359678 |
|
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PCT/US15/24541 |
Apr 6, 2015 |
|
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16457816 |
|
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|
61976364 |
Apr 7, 2014 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 2019/521 20130101;
H01F 1/0302 20130101; C09K 19/54 20130101; C09K 19/38 20130101;
G02F 2001/133531 20130101; H01F 1/0018 20130101; G02F 1/133553
20130101; G02F 1/133528 20130101; G02F 1/141 20130101; H01F 1/0081
20130101; B82Y 20/00 20130101; G02F 1/0036 20130101; B82Y 40/00
20130101; G02F 1/13768 20130101 |
International
Class: |
G02F 1/137 20060101
G02F001/137; H01F 1/00 20060101 H01F001/00; G02F 1/1335 20060101
G02F001/1335; C09K 19/54 20060101 C09K019/54; C09K 19/38 20060101
C09K019/38; G02F 1/00 20060101 G02F001/00 |
Goverment Interests
STATEMENT OF GOVERNMENTAL SUPPORT
[0002] This work was supported in part by Grant No DNR00956081 from
the National Science Foundation. The Government has certain rights
in this invention.
Claims
1-91 (canceled)
92. A method of making a thin film patterned with one or more
optical polarizations, said method comprising: providing a
substrate having deposited thereon a resin containing magnetic
nanorods, where said magnetic nanorods are coated with a silica
and/or polymer layer and form a stable colloidal dispersion, where
said magnetic nanorods function as a liquid crystal that performs
optical switching in response to a magnetic field; applying a
magnetic field to said resin to align said magnetic nanorods in all
or in one or more regions of said substrate coated with said resin;
and curing/crosslinking said resin in all or in one or more regions
of said substrate coated with said resin to fix said magnetic
nanorods in a first alignment thereby providing a first optical
polarization.
93. The method of claim 92, further comprising: applying a magnetic
field to a second region of said substrate to align magnetic
nanorods in said second region in an orientation different than
said first alignment; and curing/crosslinking said resin in said
second region to fix the magnetic nanorods aligned in the second
region in a second alignment to provide a second optical
polarization.
94. The method of claim 92, further comprising: applying a magnetic
field to a third region of said substrate to align said magnetic
nanorods in said third region in an orientation different than said
first alignment and/or said second alignment; and
curing/crosslinking said resin in third second region to fix the
magnetic nanorods aligned in the third region in a third alignment
to provide a third optical polarization.
95. The method of claim 92, wherein said method comprises leaving
the resin in one or more regions uncured/uncrosslinked so that the
magnetic nanorods in said regions reorient when a magnetic field is
applied to said film.
96. The method of claim 92, wherein said resin is a UV cured resin
and said curing/crosslinking by application of UV light to the
region that is to be cured/cross-linked.
97. The method of claim 96, wherein said resin is selected from the
group consisting of bisphenol-A-diglycidyl-ether-diacrylate (B
GEDA), polyethylene-glycoldiacrylate (PEGDA), and
poly(diethylene-glycol-carbonate):diacrylate (PGCDA).
98. The method of claim 92, wherein said resin is a chemically
cured resin and said curing/crosslinking by application of the
curing catalyst to the region that is to be cured/cross-linked.
99. The method of claim 98, wherein said catalyst is inkjet
nanoprinted on the region(s) to be cured.
100. A thin film patterned with one or more optical polarizations,
said thin film comprising: magnetic nanorods, where said magnetic
nanorods are coated with a silica and/or polymer layer and form a
stable colloidal dispersion, where said magnetic nanorods function
as a liquid crystal that performs optical switching in response to
a magnetic field, and where the magnetic nanorods are disposed in
one or more predetermined orientations at different locations in
said thin film.
101. The thin film of claim 100, wherein said film comprises one or
more first regions comprising magnetic nanorods aligned in a first
alignment providing a first polarization.
102. The thin film of claim 101, wherein said film comprises one or
more second regions comprising magnetic nanorods aligned in a
second alignment different from said first alignment providing a
second polarization different from said first polarization.
103. The thin film of claim 102, wherein said film comprises one or
more third regions comprising magnetic nanorods aligned in a third
alignment different from said first and/or said second alignment
providing a third polarization different from said first and/or
said second polarization.
104. The thin film of claim 100, wherein said film comprises one or
more regions wherein the magnetic nanorods in said regions are free
to reorient when a magnetic field is applied to said film.
105. The thin film of claim 100, wherein said film is made
according to the method of claim 92.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. Ser. No.
15/301,699, filed on Oct. 3, 2016, which is a US 371 National Phase
of PCT/US2015/024541, filed on Apr. 6, 2015, which claims benefit
of and priority to U.S. Ser. No. 61/976,364, filed on Apr. 7, 2014,
all of which are incorporated herein by reference in their entirety
for all purposes.
BACKGROUND
[0003] Development of magnetic-responsive liquid crystals (LCs) is
of both fundamental and practical importance since it not only
represents an ideal system in condensed matter that allows
exploration of phase complexity in a single sample as the external
field changes, but it also opens the way towards various
applications that benefit from the instantaneous and contactless
nature of magnetic interactions.
[0004] Conventional liquid crystals (LCs) are mostly insensitive to
magnetic fields. Limited by the low magnetic susceptibility of
their components, most studies on previous liquid crystals focus
only on the phase behavior of LCs under magnetic fields. It is
believed the use of magnetically tunable liquid crystals for
practical applications, such as optical switching, has never been
demonstrated.
SUMMARY
[0005] In various embodiments magnetically actuated liquid crystals
are provided as well as method of making the magnetically actuated
liquid crystals, methods of using the magnetically actuated liquid
crystals (e.g., in optical switching applications, displays,
anti-counterfeiting devices and the like), methods of fixing the
orientation of the components in the liquid crystals and producing
patterns of polarization in the fixed liquid crystals, and devices
comprising the magnetically actuated liquid crystals. In certain
embodiments the liquid crystals comprise magnetic anisotropic
nanostructures (e.g., nanorods) whose surfaces are modified for
dispersion if necessary, e.g., coated with a polymer or a silica
layer. In certain embodiments the nanostructures are coated with a
layer of silica.
[0006] In one illustrative, but non-limiting embodiment, liquid
crystals are provided that comprise Fe.sub.3O.sub.4 nanorods where
the nanorods are coated with a silica coating. In certain
embodiments the nanorods are provided as a suspension and/or
dispersion.
[0007] Various embodiments contemplated herein may include, but
need not be limited to, one or more of the following:
[0008] Embodiment 1: A liquid crystal, said liquid crystal
including: a suspension/dispersion of magnetic anisotropic
nanostructures.
[0009] Embodiment 2: The liquid crystal of embodiment 1, wherein
said anisotropic nanostructure includes a material selected from
the group consisting of a ferromagnetic material, a ferromagnetic
material, and a superparamagnetic material.
[0010] Embodiment 3: The liquid crystal according to any one of
embodiments 1-2, wherein said anisotropic nanostructure includes a
material selected from the group consisting of metallic iron,
metallic cobalt, metallic nickel, metallic gadolinium, metallic
dysprosium, an alloy containing iron, an alloy containing cobalt,
an alloy containing nickel, an alloy containing gadolinium, an
alloy containing dysprosium, an oxide of iron, an oxide of cobalt,
an oxide of nickel, an oxide of manganese, an oxide of europium,
and an oxide of chromium.
[0011] Embodiment 4: The liquid crystal of embodiment 2, wherein
said lanisotropic nanostructure includes Fe.sub.3O.sub.4.
[0012] Embodiment 5: The liquid crystal according to any one of
embodiments 1-4, wherein said anisotropic structures comprise
anisotropic nanostructures selected from the group consisting of
nanorods, nanoplates, nanotubes, and nanodiscs.
[0013] Embodiment 6: The liquid crystal according to any one of
embodiments 1-4, wherein said anisotropic structures comprise
nanorods.
[0014] Embodiment 7: The liquid crystal according to any one of
embodiments 1-6, wherein the average length of the long axis of
said anisotropic structures ranges from about 20 nm up to about 10
.mu.m.
[0015] Embodiment 8: The liquid crystal of embodiment 7, wherein
the average length of the long axis of said anisotropic structures
ranges from about 50 nm up to about 10 .mu.m, or from about 100 nm
up to about 5 .mu.m.
[0016] Embodiment 9: The liquid crystal of embodiment 7, wherein
the average length of the long axis of said anisotropic structures
ranges from about 20 nm, or from about 50 nm, or from about 100 nm,
or from about 200 nm, or from about 300 nm, or from about 400 nm,
or from about 500 nm up to about 10 .mu.m, up to about 5 .mu.m, or
up to about 4 .mu.m, or up to about 3 .mu.m, or up to about 2
.mu.m.
[0017] Embodiment 10: The liquid crystal of embodiment 7, wherein
the average length of the long axis of said structures is about 1.5
.mu.m.
[0018] Embodiment 11: The liquid crystal according to any one of
embodiments 1-10, wherein the average length of the short axis of
said anisotropic structures ranges from about 2 nm up to about 1
.mu.m, or from about 100 nm up to about 500 nm, or from about 100
nm up to about 300 nm.
[0019] Embodiment 12: The liquid crystal according to any one of
embodiments 1-10, wherein the average length of the short axis of
said anisotropic structures ranges from about 2 nm or from about 5
nm, or from about 10 nm, or from about 20 nm, or from about 30 nm,
or from about 40 nm, or from about 50 nm, or from about 60 nm, or
from about 70 nm, or from about 80 nm, or from about 90 nm, or from
about 100 nm, up to about 1 .mu.m, or up to about 800 nm, or up to
about 500 nm, or up to about 400 nm, or up to about 300 nm.
[0020] Embodiment 13: The liquid crystal according to any one of
embodiments 1-10, wherein the average length of the short axis of
said anisotropic structures is about 200 nm.
[0021] Embodiment 14: The liquid crystal according to any one of
embodiments 1-13, wherein the ratio of the length of the long axis
to the length of the short axis of said anisotropic structures is
at least about 1.1 or at least about 1.2, or at least about 1.3, or
at least about 1.5, or at least about 2, or at least about 3, or at
least about 4, or at least about 5, or at least about 6, or at
least about 7, or at least about 8, or at least about 9, or at
least about 10, or at least about 11, or at least about 12, or at
least about 13, or at least about 14, or at least about 15, or at
least about 16, or at least about 17, or at least about 18, or at
least about 19, or at least about 20.
[0022] Embodiment 15: The liquid crystal according to any one of
embodiments 1-14, wherein the surface of said nanostructures is
modified to ensure dispersion/suspension in a solvent.
[0023] Embodiment 16: The liquid crystal of embodiment 15, wherein
the surface of said nanostructure is functionalized with a
hydrophilic group.
[0024] Embodiment 17: The liquid crystal of embodiment 16, wherein
the surface of said nanostructure is functionalized with a group
selected from the group consisting of hydroxyl, carboxyl,
sulfhydryl, carbonyl, amino, and phosphate.
[0025] Embodiment 18: The liquid crystal of embodiment 15, wherein
the surface of said nanostructure has a polymer layer or a silica
layer thereon.
[0026] Embodiment 19: The liquid crystal of embodiment 15, wherein
the surface of said nanostructure has a silica layer thereon.
[0027] Embodiment 20: The liquid crystal according to any one of
embodiments 1-19, wherein said anisotropic nanostructures are
suspended/dispersed in a polar solvent, a non-polar solvent, or a
mixture of polar and non-polar solvents.
[0028] Embodiment 21: The liquid crystal of embodiment 26, wherein
said anisotropic nanostructures are suspended/dispersed in a polar
solvent.
[0029] Embodiment 22: The liquid crystal of embodiment 26, wherein
said anisotropic nanostructures are suspended/dispersed in a
solution including water.
[0030] Embodiment 23: The liquid crystal of embodiment 26, wherein
said anisotropic nanostructures are suspended/dispersed in a
solution including an alcohol.
[0031] Embodiment 24: The liquid crystal of embodiment 23, wherein
said anisotropic nanostructures are suspended/dispersed in a
solution including an alcohol selected from the group consisting of
methanol, ethanol, propanol, 1-butanol, 2-butanol, 2-methyl-1
propanol, 2-methyl-2-propanol, ethylene glycol, methylene glycol,
propylene glycol, glycerol, benzyl alcohol, cinnamic alcohol,
diethylene glycol, grandisol, cyclohexanol, and octanol.
[0032] Embodiment 25: The liquid crystal of embodiment 23, wherein
said anisotropic nanostructures are suspended/dispersed in a
solution including ethylene glycol.
[0033] Embodiment 26: The liquid crystal of embodiment 23, wherein
said anisotropic nanostructures are suspended/dispersed in a
non-polar solvent.
[0034] Embodiment 27: The liquid crystal according to any one of
embodiments 1-26, wherein the volume fraction of anisotropic
nanostructures in said suspension/dispersion is greater than about
0.1%.
[0035] Embodiment 28: The liquid crystal of embodiment 27, wherein
the volume fraction of anisotropic nanostructures in said
suspension/dispersion ranges from about 0.1% up to about 70%.
[0036] Embodiment 29: The liquid crystal according to any one of
embodiments 27-28, wherein the volume fraction of anisotropic
nanostructures in said suspension/dispersion is greater than about
0.5%, or greater than about 1%, or greater than about 3%, or
greater than about 4%, or greater than about 3%, or greater than
about 5%, or greater than about 6%, or greater than about 7%, or
greater than about 8%, or greater than about 9%, or greater than
about 10%, or greater than about 11%, or greater than about 12%, or
greater than about 13%, or greater than about 14%, or greater than
about 15%, or greater than about 16%, or greater than about 17%, or
greater than about 18%, or greater than about 19%, or greater than
about 20%.
[0037] Embodiment 30: The liquid crystal according to any one of
embodiments 1-26, wherein the volume fraction of anisotropic
nanostructures in said suspension/dispersion is about 10%.
[0038] Embodiment 31: The liquid crystal according to any one of
embodiments 27-30, wherein the volume fraction of anisotropic
structures in said suspension is sufficient to provide ordered
liquid crystalline phases.
[0039] Embodiment 32: The liquid crystal according to any one of
embodiments 1-31, wherein the anisotropic structures reorient in a
magnetic field having intensity less than about 1T.
[0040] Embodiment 33: The liquid crystal of embodiment 32, wherein
the anisotropic structures reorient in a magnetic field having an
intensity less than about 800 mT, or less than bout 500 mT, or less
than about 400 mT, or less than about 300 mT, or less than about
200 mT, or less than about 100 mT, or less than about 50 mT, or
less than about 25 mT, or less than about 10 mT, or less than about
5 mT, or at about 1 mT.
[0041] Embodiment 34: The liquid crystal according to any one of
embodiments 1-33, wherein the anisotropic structures are
suspended/dispersed in a solution containing polymer or pre-polymer
molecules.
[0042] Embodiment 35: A device including: a first polarizing layer
or film configured to act as a polarizer; a second polarizing layer
or film; and a liquid crystal according to any one of embodiments
1-34 disposed between said first polarizing layer or film and said
second polarizing layer or film.
[0043] Embodiment 36: The device of embodiment 35, wherein said
first polarizing layer or film is configured to act as a
polarizer.
[0044] Embodiment 37: The device of according to any one of
embodiments 35-36, wherein said second polarizing layer or film is
configured to act as an analyzer.
[0045] Embodiment 38: The device of according to any one of
embodiments 35-37, wherein the angle of polarization of said first
polarizing layer or film differs from the angle of polarization of
said second polarizing layer or film.
[0046] Embodiment 39: The device of embodiment 38, wherein the
angle of polarization of said first polarizing layer or film and
the angle of said second polarizing layer or film differ by an
amount that ranges from about 0 degrees to about 180 degrees.
[0047] Embodiment 40: The device of embodiment 39, wherein the
angle of polarization of said first polarizing layer or film and
the angle of said second polarizing layer or film differ by about
45 degrees.
[0048] Embodiment 41: The device of embodiment 39, wherein the
angle of polarization of said first polarizing layer or film and
the angle of said second polarizing layer or film differ by about
90 degrees.
[0049] Embodiment 42: The device of according to any one of
embodiments 35-41, wherein said device further includes a
reflective layer disposed behind said first polarizing layer or
film and sais second polarizing layer or film.
[0050] Embodiment 43: The device of according to any one of
embodiments 35-42, wherein said device is a component of an
apparatus selected from the group consisting of a display, a
waveguide, an actuator, and an optical modulator.
[0051] Embodiment 44: A method of optical switching, said method
including: passing a polarized optical signal through a liquid
crystal according to any one of embodiments 1-34; and applying a
magnetic field to said liquid crystal to alter the transmission of
said liquid crystal to said optical signal.
[0052] Embodiment 45: The method of embodiment 44, wherein said
magnetic field is switched at a frequency of at least 1 Hz.
[0053] Embodiment 46: The method of embodiment 45, wherein said
magnetic field is switched at a frequency of at least 5 Hz, or at
least 10 Hz, or at least 20 Hz, or at least 50 Hz, or at least 80
Hz, or at least 100 Hz, or at least 150 Hz, or at least 200 Hz.
[0054] Embodiment 47: The method according to any one of
embodiments 44-46, wherein said method is performed using a device
according to any one of embodiments 35-43.
[0055] Embodiment 48: A method of fabricating magnetic anisotropic
nanostructures for use as magnetic liquid crystals, said method
including: preparing nonmagnetic anisotropic nanostructures;
modifying the surface of said nanostructures if necessary to ensure
solvent dispersity; and converting said nanostructures into
magnetic anisotropic nanostructures.
[0056] Embodiment 49: A method of fabricating magnetic anisotropic
nanostructures for use as magnetic liquid crystals, said method
including: preparing magnetic anisotropic nanostructures; and
modifying the surface of said nanostructures if necessary to ensure
solvent dispersity.
[0057] Embodiment 50: The method of embodiment 49, wherein said
anisotropic structures comprise a material selected from the group
consisting of metallic iron, metallic cobalt, metallic nickel,
metallic gadolinium, metallic dysprosium, an alloy containing iron,
an alloy containing cobalt, an alloy containing nickel, an alloy
containing gadolinium, an alloy containing dysprosium, an oxide of
iron, an oxide of cobalt, an oxide of nickel, an oxide of
manganese, an oxide of europium, and an oxide of chromium.
[0058] Embodiment 51: The method of embodiment 49, wherein said
anisotropic structures comprise a material selected from the group
consisting of Fe, Co, Ni, Mn, Gd, Dy, Eu, Cr, Zn, Cu, Mg, O, Si,
Bi, Y, Sb.
[0059] Embodiment 52: The method of embodiment 49, wherein said
anisotropic structures comprise a material selected from the group
consisting of compounds of Fe, Co, Ni, Mn, Gd, Dy, Eu, Cr, Zn, Cu,
Mg, O, Si, Bi, Y, Sb.
[0060] Embodiment 53: The method of embodiment 49, wherein said
anisotropic structures comprise a material selected from the group
consisting of alloys of Fe, Co, Ni, Mn, Gd, Dy, Eu, Cr, Zn, Cu, Mg,
O, Si, Bi, Y, Sb.
[0061] Embodiment 54: The method of embodiment 49, wherein said
anisotropic structures comprise includes Fe.sub.3O.sub.4.
[0062] Embodiment 55: The method according to any one of
embodiments 49-54, wherein said anisotropic structures comprise
anisotropic nanostructures selected from the group consisting of
nanorods, nanoplates, nanotubes, and nanodiscs.
[0063] Embodiment 56: The method according to any one of
embodiments 49-54, wherein said anisotropic structures comprise
nanorods.
[0064] Embodiment 57: The method according to any one of
embodiments 49-56, wherein the average length of the long axis of
said anisotropic structures ranges from about 20 nm up to about 10
.mu.m.
[0065] Embodiment 58: The method of embodiment 57, wherein the
average length of the long axis of said anisotropic structures
ranges from about 50 nm up to about 10 .mu.m, or from about 100 nm
up to about 5 .mu.m.
[0066] Embodiment 59: The method of embodiment 57, wherein the
average length of the long axis of said anisotropic structures
ranges from about 20 nm, or from about 50 nm, or from about 100 nm,
or from about 200 nm, or from about 300 nm, or from about 400 nm,
or from about 500 nm up to about 10 .mu.m, up to about 5 .mu.m, or
up to about 4 .mu.m, or up to about 3 .mu.m, or up to about 2
.mu.m.
[0067] Embodiment 60: The method of embodiment 57, wherein the
average length of the long axis of said structures is about 1.5
.mu.m.
[0068] Embodiment 61: The method according to any one of
embodiments 49-60, wherein the average length of the short axis of
said anisotropic structures ranges from about 2 nm up to about 1
.mu.m, or from about 100 nm up to about 500 nm, or from about 100
nm up to about 300 nm.
[0069] Embodiment 62: The method according to any one of
embodiments 49-60, wherein the average length of the short axis of
said anisotropic structures ranges from about 2 nm or from about 5
nm, or from about 10 nm, or from about 20 nm, or from about 30 nm,
or from about 40 nm, or from about 50 nm, or from about 60 nm, or
from about 70 nm, or from about 80 nm, or from about 90 nm, or from
about 100 nm, up to about 1 .mu.m, or up to about 800 nm, or up to
about 500 nm, or up to about 400 nm, or up to about 300 nm.
[0070] Embodiment 63: The method according to any one of
embodiments 49-60, wherein the average length of the short axis of
said anisotropic structures is about 200 nm.
[0071] Embodiment 64: The method according to any one of
embodiments 49-63, wherein the ratio of the length of the long axis
to the length of the short axis of said anisotropic structures is
at least about 1.1 or at least about 1.2, or at least about 1.3, or
at least about 1.5, or at least about 2, or at least about 3, or at
least about 4, or at least about 5, or at least about 6, or at
least about 7, or at least about 8, or at least about 9, or at
least about 10, or at least about 11, or at least about 12, or at
least about 13, or at least about 14, or at least about 15, or at
least about 16, or at least about 17, or at least about 18, or at
least about 19, or at least about 20.
[0072] Embodiment 65: The method according to any one of
embodiments 49-64, wherein said preparing includes preparing
nanostructures including FeOOH nanostructures including an
FeCl.sub.3 precursor.
[0073] Embodiment 66: The method according to any one of
embodiments 49-65, wherein said modifying the surface of said
nanostructures includes modifying said surface with a
surfactant.
[0074] Embodiment 67: The method according to any one of
embodiments 49-65, wherein said modifying the surface of said
nanostructures includes functionalizing said surface with a
hydophylic group.
[0075] Embodiment 68: The method of embodiment 67, wherein said
modifying the surface of said nanostructures includes
functionalizing said surface with a group selected from the group
consisting of hydroxyl, carboxyl, sulfhydryl, carbonyl, amino, and
phosphate.
[0076] Embodiment 69: The method according to any one of
embodiments 49-65, wherein said modifying the surface of said
nanostructures includes coating said surface with an oxide
coating.
[0077] Embodiment 70: The method of embodiment 69, wherein said
oxide coating includes silica.
[0078] Embodiment 71: The method of embodiment 70, wherein said
modifying the surface of said nanostructures includes reacting said
nanostructures with a silica alkoxide.
[0079] Embodiment 72: The method of embodiment 71, wherein said
modifying the surface of said nanostructures includes reacting said
nanostructures with a silica alkoxide selected from the group
consisting of tetraethyl orthosilicate (TEOS), and tetramethyl
orthosilicate (TMOS).
[0080] Embodiment 73: The method according to any one of
embodiments 49-65, wherein said modifying the surface of said
nanostructures includes coating said surface with a polymer
coating.
[0081] Embodiment 74: The method according to any one of
embodiments 48, and 50-73, wherein said converting said modified
nanostructures into magnetic anisotropic nanostructures includes
reducing said non-magnetic nanostructures.
[0082] Embodiment 75: The method according to any one of
embodiments 48, and 50-73, wherein said converting said modified
nanostructures into magnetic anisotropic nanostructures includes
reducing FeOOH in said nanostructures to Fe.sub.3O.sub.4.
[0083] Embodiment 76: The method according to any one of
embodiments 74-75, wherein said reducing is performed using a
material selected from the group consisting of diethylene glycol,
ethylene glycol, glycerol, borohydride, hydrazine, and
hydrogen.
[0084] Embodiment 77: The method according to any one of
embodiments 48-76, wherein said method further includes purifying
and/or concentrating said magnetic anisotropic nanostructures.
[0085] Embodiment 78: The method of embodiment 77, wherein said
purifying and/or concentrating includes one or more magnetic
separation steps.
[0086] Embodiment 79: The method according to any one of
embodiments 48-78, wherein said magnetic anisotropic nanostructures
are concentrated or resuspended to a volume fraction greater than
about 0.1%.
[0087] Embodiment 80: The method according to any one of
embodiments 48-78, wherein said magnetic anisotropic nanostructures
are concentrated or resuspended to a volume fraction that ranges
0.1% up to about 70%.
[0088] Embodiment 81: The method according to any one of
embodiments 48-78, wherein said magnetic anisotropic nanostructures
are concentrated or re-suspended to a volume fraction that is
greater than about 0.5%, or greater than about 1%, or greater than
about 3%, or greater than about 4%, or greater than about 3%, or
greater than about 5%, or greater than about 6%, or greater than
about 7%, or greater than about 8%, or greater than about 9%, or
greater than about 10%, or greater than about 11%, or greater than
about 12%, or greater than about 13%, or greater than about 14%, or
greater than about 15%, or greater than about 16%, or greater than
about 17%, or greater than about 18%, or greater than about 19%, or
greater than about 20%.
[0089] Embodiment 82: The method according to any one of
embodiments 48-78, wherein said magnetic anisotropic nanostructures
are concentrated or re-suspended to a volume fraction sufficient to
provide ordered liquid crystalline phases.
[0090] Embodiment 83: The method according to any one of
embodiments 48-82, wherein said anisotropic nanostructures are
suspended in a polar solvent, a non-polar solvent, or a mixture of
polar and non-polar solvents.
[0091] Embodiment 84: The method of embodiment 83, wherein said
anisotropic nanostructures are suspended in a polar solvent.
[0092] Embodiment 85: The method of embodiment 83, wherein said
anisotropic nanostructures are suspended in a solution including
water.
[0093] Embodiment 86: The method of embodiment 83, wherein said
anisotropic nanostructures are suspended in a solution including an
alcohol.
[0094] Embodiment 87: The method of embodiment 86, wherein said
anisotropic nanostructures are suspended in a solution including an
alcohol selected from the group consisting of methanol, ethanol,
propanol, 1-butanol, 2-butanol, 2-methyl-1 propanol,
2-methyl-2-propanol, ethylene glycol, methylene glycol, propylene
glycol, glycerol, benzyl alcohol, cinnamic alcohol, diethylene
glycol, grandisol, cyclohexanol, and octanol.
[0095] Embodiment 88: The method of embodiment 86, wherein said
anisotropic nanostructures are suspended in a solution including
ethylene glycol.
[0096] Embodiment 89: The method of embodiment 83, wherein said
anisotropic nanostructures are suspended in a non-polar
solvent.
[0097] Embodiment 90: The method of embodiment 83, wherein the
anisotropic structures are suspended in a solution containing
polymer or pre-polymer molecules.
[0098] Embodiment 91: A liquid crystal including silica-coated
magnetic anisotropic nanostructures fabricated according to the
method of any one of embodiments 48-90.
[0099] Embodiment 92: A method of making a thin film patterned with
one or more optical polarizations, said method including: providing
a substrate having deposited thereon a resin containing anisotropic
magnetic nanostructures as recited in any one of embodiments 1-34;
applying a magnetic field to said resin to align said anisotropic
magnetic nanostructures in all or in one or more regions of said
substrate coated with said resin; and curing/crosslinking said
resin in all or in one or more regions of said substrate coated
with said resin to fix said anisotropic magnetic nanostructures in
a first alignment thereby providing a first optical
polarization.
[0100] Embodiment 93: The method of embodiment 92, further
including: applying a magnetic field to a second region of said
substrate to align anisotropic magnetic nanostructures in said
second region in an orientation different than said first
alignment; and curing/crosslinking said resin in said second region
to fix the anisotropic magnetic nanostructures aligned in the
second region in a second alignment to provide a second optical
polarization.
[0101] Embodiment 94: The method according to any one of
embodiments 92-93, further including: applying a magnetic field to
a third region of said substrate to align said anisotropic magnetic
nanostructures in said third region in an orientation different
than said first alignment and/or said second alignment; and
curing/crosslinking said resin in third second region to fix the
nanorods aligned in the third region in a third alignment to
provide a third optical polarization.
[0102] Embodiment 95: The method according to any one of
embodiments 92-94, wherein said method includes leaving the resin
in one or more regions uncured/uncrosslinked so that the
anisotropic magnetic nanostructures in said regions reorient when a
magnetic field is applied to said film.
[0103] Embodiment 96: The method according to any one of
embodiments 92-95, wherein said resin is a UV cured resin and said
curing/crosslinking by application of UV light to the region that
is to be cured/cross-linked.
[0104] Embodiment 97: The method of embodiment 96, wherein said
resin is selected from the group consisting of
bisphenol-A-diglycidyl-ether-diacrylate (BGEDA),
polyethylene-glycol-diacrylate (PEGDA), and
poly(diethylene-glycol-carbonate) diacrylate (PGCDA).
[0105] Embodiment 98: The method according to any one of
embodiments 92-95, wherein said resin is a chemically cured resin
and said curing/crosslinking by application of the curing catalyst
to the region that is to be cured/cross-linked.
[0106] Embodiment 99: The method of embodiment 98, wherein said
catalyst is inkjet nanoprinted on the region(s) to be cured.
[0107] Embodiment 100: A thin film patterned with one or more
optical polarizations, said thin film including: anisotropic
magnetic nanostructures as recited in any one of embodiments 1-34,
where the anisotropic magnetic nanostructures are disposed in one
or more predetermined orientations at different locations in said
thin film.
[0108] Embodiment 101: The thin film of embodiment 100, wherein
said film includes one or more first regions including anisotropic
magnetic nanostructures aligned in a first alignment providing a
first polarization.
[0109] Embodiment 102: The thin film of embodiment 101, wherein
said film includes one or more second regions including anisotropic
magnetic nanostructures aligned in a second alignment different
from said first alignment providing a second polarization different
from said first polarization.
[0110] Embodiment 103: The thin film of embodiment 102, wherein
said film includes one or more third regions including anisotropic
magnetic nanostructures aligned in a third alignment different from
said first and/or said second alignment providing a third
polarization different from said first and/or said second
polarization.
[0111] Embodiment 104: The thin film according to any one of
embodiments 100-103, wherein said film includes one or more regions
wherein the anisotropic magnetic nanostructures in said regions are
free to reorient when a magnetic field is applied to said film.
[0112] Embodiment 105: The thin film according to any one of
embodiments 100-104, wherein said film is made according to the
method of any one of embodiments 92-99.
BRIEF DESCRIPTION OF THE DRAWINGS
[0113] FIG. 1 shows TEM images of (panel a) FeOOH nanorods and
(panel b) Fe.sub.3O.sub.4@SiO.sub.2 nanorods. Scale bars: 1 .mu.m;
(panel c) magnetic hysteresis loop of Fe.sub.3O.sub.4@SiO.sub.2
nanorods; (panel d) SEM image of a fixed magnetic liquid crystal in
a polymer matrix showing the ordered arrangement of magnetic
nanorods. Scale bars: 1 .mu.m; (panel e) POM images of aqueous
dispersions of Fe.sub.3O.sub.4@SiO.sub.2 nanorods in a capillary
tube at different volume fractions (.PHI.) of 1%, 3%, 5% and 10%
(from top to bottom). Scale bars: 500 .mu.m.
[0114] FIG. 2, (panels a-d) POM images and (panels e-h)
bright-field OM images of a magnetic liquid crystal film under
magnetic fields oriented in different directions. Black arrows at
the top-left indicate the transmission axis of the polarizer (P)
and analyzer (A). White arrows indicate the field direction. The
top-right corner in each image contains no sample. Scale bars: 500
.mu.m.
[0115] FIG. 3 (panel a) Scheme showing the optical switching
process, and (panel b) the transmittance intensity profile of a
magnetic liquid crystal under an alternating magnetic field.
[0116] FIG. 4 (panel a) Scheme showing the lithography process for
the fabrication of thin films with patterns of different
polarizations; (panels b-d) POM images of various
polarization-modulated patterns; (panel e) enlarged OM image shows
the arrangement of nanorods in the pattern (left) and surrounding
area (right). Scale bars: (panels b-d) 500 .mu.m;(panel e) 10
.mu.m
[0117] FIG. 5 (panels a-d) POM images of two polarization-modulated
patterns under cross polarizers before (panels a,b) and after
(panels c,d) shifting the direction of the transmission axis of the
polarizers for 45.degree.; (panels e,f) bright-field images of the
same patterns; (panel g) plot showing the dependence of the
transmittance of the thin film on the angle between the nanorod
orientation and the transmission axis of the polarizer; (panel h)
POM image of a single thin film patterned with different brightness
in different areas by controlling the relative orientation of the
nanorods, which is indicated by the white arrows. Scale bars: 500
.mu.m.
DEFINITIONS
[0118] The terms "suspension" and "dispersion" are used
interchangeably herein to refer to nanostructures present in a
fluid (or polymerized) medium. In certain embodiments the
nanostructures are homogenously dispersed in the medium, while in
other embodiments, the nanostructures are not homogenously
dispersed. In certain embodiments the nanoparticle provide one or a
plurality of phases in the medium.
DETAILED DESCRIPTION
[0119] In various embodiments magnetically actuated liquid crystals
are provided as well as method of making the magnetically actuated
liquid crystals, methods of using the liquid crystals (e.g., in
optical switching applications, displays, and the like), and
devices comprising the liquid crystals. In certain embodiments the
liquid crystals comprise magnetic anisotropic nanostructures (e.g.,
nanorods and nanoplates). If necessary, the surfaces of these
magnetic anisotropic nanostructures are modified with additional
coating for enhanced dispersion in solvents, e.g., coated with a
layer of capping ligands, or polymer, or inorganic oxides such as
silica. In certain embodiments the nanostructures are coated with a
silica layer.
[0120] In one illustrative, but non-limiting embodiment for the
fabrication of liquid crystals, superparamagnetic iron oxide
nanorods or nanoplates are synthesized, and their surfaces are
modified with capping ligands, or oxide such as silica, or polymer
for enhanced dispersion (if necessary). The nanorods or nanoplates
can be dispersed in a suitable solvent at a certain volume fraction
to form magnetically actuated liquid crystals. These liquid
crystals show an outstanding magnetic response and
magnetic-field-controlled instant and reversible orientation.
[0121] In one illustrative, but non-liming embodiment, for the
fabrication of liquid crystals, ferrimagnetic iron oxide nanorods
or nanoplates are synthesized, and their surfaces modified with
capping ligands, or oxide such as silica, or polymer for enhanced
dispersion (if necessary). Then they were dispersed in suitable
solvent at a certain volume fraction to form magnetically actuated
liquid crystals. These liquid crystals show an outstanding magnetic
response and magnetic-field-controlled instant and reversible
orientation.
[0122] In one illustrative but non-limiting embodiment, nonmagnetic
FeOOH nanorods ARE first synthesized, followed by a coating of
silica on their surfaces, and are finally reduced to
superparamagnetic or ferrimagnetic iron oxide nanorods encapsulated
in a silica layer by diethylene glycol at elevated temperature. The
as-reduced nanorods can be dispersed in water or polar solvent at a
certain volume fraction, e.g., 10%, and magnetically to provide
actuated liquid crystals. Dependent on the volume fraction, this
liquid crystal can form nematic or smectic phases. These liquid
crystals show an outstanding magnetic response and
magnetic-field-controlled instant and reversible orientation tuning
is demonstrated.
[0123] In one illustrative, but non-liming embodiment, for the
fabrication of liquid crystals,nonmagnetic Ni(OH).sub.2 nanoplates
are first synthesized, followed by a coating of SiO.sub.2 on their
surfaces, and finally reduced to Fe.sub.3O.sub.4@SiO.sub.2 nanorods
by hydrogen. The as-reduced nanoplates were dispersed in water or
polar solvent at a certain volume fraction, and magnetically
actuated liquid crystals were achieved. Dependent on the volume
fraction, this liquid crystal can form nematic or columnar or
hexagonal phases. These liquid crystals show an outstanding
magnetic response and magnetic-field-controlled instant and
reversible orientation.
[0124] In one illustrative, but non-liming embodiment, for the
fabrication of liquid crystals, nonmagnetic nanorods or nanoplates
were first synthesized, followed by a coating of polymer on their
surfaces, and were finally reduced to ferromagnetic core@polymer
nanostructures. The as-reduced nanostructures were dispersed in
water or polar solvent at a certain volume fraction to form
magnetically actuated liquid crystals. These liquid crystals show
an outstanding magnetic response and magnetic-field-controlled
instant and reversible orientation.
[0125] In one illustrative, but non-liming embodiment, for the
application of magnetically actuated liquid crystals in displays,
but non-limiting embodiment, magnetically actuated liquid crystals
were sandwiched between cross polarizers to form a device. As the
field direction changes, this device can tune the transmittance of
light. An alternating magnetic field was applied to the device
(e.g., 5 mT), the liquid crystal exhibited an optical switching
frequency of above 100 Hz, which is comparable to commercial liquid
crystals and thus can be a promising substitute for them in device
applications. Color filters are attached to this device to create a
proto-type of magnetically responsive liquid crystal color
display.
[0126] In one illustrative, but non-liming embodiment, for the
application of magnetically actuated liquid crystals in
polarization pattern printing, but non-limiting embodiment,
magnetically actuated liquid crystals were mixed with photocurable
polymer precursors, and sandwiched between glasses. A mask was
applied to the sample; liquid crystals in selected areas were cured
by ultraviolet light and their orientations were fixed with the aid
of magnetic fields. The mask was then removed to allow the curing
of liquid crystals in the rest areas and the fixing of their
orientation in a different direction with the aid of magnetic
fields. This process can be repeated for multiple times for the
creation of complex patterns.
EXAMPLES
[0127] The following examples are offered to illustrate, but not to
limit the claimed invention.
Example 1
Magnetically Actuated Liquid Crystals
[0128] The liquid-like behavior and optical anisotropy of liquid
crystals have catalyzed many important applications in modern
technology. Their molecular order can be manipulated through
external stimuli such as temperature change and electric and
magnetic fields, therefore enabling many technological advances,
with a particularly successful example being the liquid crystal
displays driven by electric fields. Although conventional liquid
crystals may be sensitive to magnetic fields, the low magnetic
susceptibility of molecular species makes practical applications
difficult as extremely strong magnetic fields are required to
enable effective switching of the molecular order (Kneppe et al.
(1982) Chem. Phys. Lett. 87: 59; Lemaire et al. (2004) Phys. Rev.
Lett. 93: 267801; van den Pol et al. (2009) Phys. Rev. Lett. 103:
160952).
[0129] Herein we demonstrate that ferrimagnetic inorganic nanorods
can be used as building blocks to construct liquid crystals with
optical properties that can be instantly and reversibly controlled
by manipulating the nanorod orientation using considerably weak
external magnetic fields. Under an alternating magnetic field (5
mT), they exhibit an optical switching frequency above 100 Hz,
which is comparable to the performance of commercial liquid
crystals based on electrical switching. Developing such
magnetically actuated liquid crystals opens the door towards
various applications, which may benefit from the instantaneous and
contactless nature of magnetic manipulation (Yang and Wu,
Fundamentals of liquid crystal devices. Wiley SID series in display
technology (John Wiley, Chichester ; Hoboken, N.J., 2006), pp. xvi,
378 p; Boamfa et al. (2005) Adv. Mater. 17: 610).
[0130] Effective switching of the optical properties of liquid
crystals using external magnetic fields has remained a great
challenge. While direct incorporation of ferro- or ferrimagnetic
materials into liquid crystals has been attempted (. Fabre et al.
(1990) Phys. Rev. Lett. 64: 539, Vallooran et al. (2011) Adv.
Mater. 23: 3932; Cordoyiannis et al. (2009) Phys. Rev. E 79), a
long interaction time is usually required to induce uniform
molecular alignment. A more straightforward strategy is to enhance
the intrinsic magnetic property of the constituents of liquid
crystals, for example, by doping rare earth metal ions into liquid
crystal molecules (Binnemans et al. (2000) J. Am. Chem. Soc. 122:
4335) or by developing alternative inorganic building blocks with a
higher magnetic susceptibility (Hijnen, and Clegg (2012) Chem.
Mater. 24: 3449). However, most such studies have been limited to
paramagnetic materials, which can only be aligned in extremely
strong external magnetic fields(>1 T). In this regard, the
direct use of ferro- or ferrimagnetic inorganic materials
represents the best solution to design magnetically responsive
liquid crystals because they have higher magnetic susceptibility
and can rapidly respond to a relatively weak magnetic field. In
such systems, the magnetic interaction energy, instead of the
nematic potential in the cases involving diamagnetic/paramagnetic
materials, dominates the orientation behavior of liquid crystals,
so that the orientational control and the optical switching can be
effectively carried out with orders of magnitude reduction in the
required field strength but with high magnetic ordering efficiency.
Onsager theoretically predicted in his pioneering work the
spontaneous nematic ordering of long hard rods in the purely
entropic regime (Onsager (1949) Ann. N. Y. Acad. Sci. 51: 627),
leaving the remaining challenges of developing a controlled
synthesis for anisotropically shaped magnetic nanostructures, and
more importantly, their effective stabilization as a liquid
dispersion because particles with net magnetic dipole moments
usually aggregate due to magnetic dipole-dipole interactions.
[0131] Studies on inorganic liquid crystals have been limited to
molecular species or highly polydisperse disk- and rod shaped
inorganic colloids such as gibbsite (Al(OH).sub.3) and boehmite
(AlO(OH)) platelets (van der Beek and Lekkerkerker (2004) Langmuir
20: 8582), platelike smectite clays (Gabriel et al. (1996) J. Phys.
Chem. 100: 11139), graphene sheets (Behabtu et al. (2010) Nat.
Nano. 5: 406), geothite nanorods (Lemaire et al. (2004) The Europ.
Phy. J. E 13: 291), GdPO.sub.4 and LaPO.sub.4 nanorods (Kim et al.
(2012) Adv. Funct. Mater. 22: 4949), or semiconductor nanorods of
CdSe (Li et al. (2002) Nano. Lett. 2: 557). Magnetic anisotropic
nanostructures with a uniform size, well defined shape, and good
solution dispersity can be synthesized using various solution phase
and gas phase deposition methods. We can also design indirect
strategies that involve the preparation of nonmagnetic anisotropic
nanostructures as precursors, surface passivation to enhance the
colloidal stability, and then conversion of the precursors into
magnetic anisotropic nanostructures. As one example, we chose FeOOH
nanorods as the starting material, which can be easily prepared
through a hydrolysis reaction. A representative transmission
electron microscopy (TEM) image of the nanorods is shown in FIG. 1,
panel a. The FeOOH nanorods were further coated with a layer of
silica through a sol-gel process, and then reduced to
Fe.sub.3O.sub.4 by diethylene glycol at 220.degree. C. As shown in
FIG. 1, panel b, the product maintains a well-defined rod-like
morphology, with an average length of 1.5 .mu.m and diameter of 200
nm. Magnetic measurement confirms the ferrimagnetic nature of the
Fe.sub.3O.sub.4 nanorods, showing a saturated magnetization of 18
emu/g and a coercivity of 300 Oe. The surface silica layer plays an
important role in the stabilization of the colloidal dispersion of
magnetic nanorods: it acts as a physical barrier to separate the
magnetic cores from each other, attenuate their magnetic
dipole-dipole interactions, and prevent them from aggregating. The
abundant hydroxyl groups on the silica surface provide sufficient
long-range electrostatic repulsion and short-range solvation forces
for stabilizing the magnetic nanorods, granting them excellent
dispersibility in various polar solvents such as water and
alcohols.
[0132] Upon the application of an external magnetic field, the
magnetic nanorods align themselves along the field direction,
producing the orientational order needed for the formation of
liquid crystals. Since the average size of the nanorods is much
larger than the detection limit of small angle X-ray scattering
measurement, resolving the crystal structure of the sample in the
magnetic field is difficult to achieve. An alternative method which
allows us to directly observe the alignment of the nanorods is to
fix the nanorods in a polymer matrix. In this case,
Fe.sub.3O.sub.4@SiO.sub.2 nanorods were dispersed in a UV curable
poly(ethylene glycol) diacrylate (PEGDA) resin at a volume fraction
(.PHI.) of 10%. Under an external magnetic field, the dispersion
was exposed to UV light to initiate polymerization. Afterwards, the
polymerized solid was cut and its cross section was examined using
scanning electron microscopy (SEM). As shown in FIG. 1, panel d, a
uniform alignment of nanorods could be observed, which confirms the
orientational order of the nanorods that leads to liquid crystal
properties, although it is still difficult to resolve positional
order by using this method. FIG. 1, panel e shows the polarized
optical microscopy (POM) images of the aqueous dispersions of
Fe.sub.3O.sub.4@SiO.sub.2 nanorods at different volume fractions
from 1% to 10%, clearly indicating a transition from an isotropic
phase to a more ordered nematic phase as the volume fraction
increased, and confirmed the liquid crystal behavior of the
dispersions.
[0133] We then demonstrated the optical tuning of such liquid
crystal by a magnetic field. The orientation of the nanorods was
found to vary with the direction of the magnetic field, resulting
in visual changes under POM. Note that the strength of the magnetic
fields used in this work is fixed at .about.10 G, unless otherwise
specified. The intensity of light transmitted through a liquid
crystal sandwiched between cross polarizers can be typically
described as:
I=I.sub.0 sin.sup.2(2.alpha.)sin.sup.2(.pi..DELTA.nL/.lamda.)
(1)
where I.sub.0 is the intensity of light passing through the first
polarizer; .alpha. is the angle between the transmission axes of
the polarizer and the long axis of the liquid crystal; .DELTA.n is
the difference in the refractive indices along the long axis and
short axis for liquid crystals aligned at a specific angle; L is
the sample thickness; and .lamda. is the wavelength of incident
light. The birefringence of the sample dispersion was measured to
be 0.15 and did not show significant change as the field strength
increased, indicating good alignment of the nanorods. When the
field direction is parallel or perpendicular to the polarizer, a is
equal to zero or 90.degree., leading to dark optical views (FIG. 2,
panels a c). As the field direction turns to 45.degree. relative to
the polarizer, a changes to 45.degree., so that the intensity
reaches the maximum according to Equation 1, resulting in bright
views, as shown in FIG. 2, panels b and d. In contrast, the
corresponding bright field optical microscopy images of the same
sample did not show apparent differences in the darkness of the
view in response to the changes in the direction of the magnetic
field, as indicated in FIG. 2, panels e-h.
[0134] The magnetic liquid crystals can rapidly respond to changes
in the direction of external magnetic fields. A video demonstrates
the continuous optical switching of a liquid crystal in a rotating
magnetic field. In order to obtain a quantitative understanding of
its switching frequency, we studied the optical properties of the
liquid crystal under a high-frequency alternating magnetic field.
Upon application of the magnetic field, the nanorods oscillate as a
result of the quick switching of field polarity from one direction
to the opposite (Zorba et al. (2010) J. Phys. Chem. C 114: 17868).
As the orientation of the nanorods is temporarily displaced from
the equilibrium position, which is parallel to the transmission
axis of the polarizer, a laser beam passes through the cross
polarizer and gives a detectable signal. The black curve in FIG. 3,
panel a, indicates that this liquid crystal exhibits a rapid
response to an alternating 5 mT field. The transmittance changes
drastically within 0.01 s, corresponding to a switching frequency
of 100 Hz, while in a control experiment, no transmittance change
is observed in the absence of the liquid crystal sample (red
curve).
[0135] One of the advantages of inorganic-nanostructure-based
liquid crystals is the possibility for convenient fixation of the
orientational order. Here we further demonstrate that thin films
patterned with various optical polarizations can be conveniently
produced by combining the magnetic liquid crystals with lithography
processes. As schematically shown in FIG. 4, panel a, a liquid
crystal solution containing magnetic nanorods and PEGDA resin was
first sandwiched between a glass cover slip and a glass slide to
form a liquid film. A photomask was then placed on top of the
sample, followed by the application of a magnetic field. Upon
exposure to UV light, the orientation of the nanorods in the
uncovered regions was fixed along a specific direction within the
plane of the film. The photomask was then removed and the sample
was again exposed to UV light in the presence of a magnetic field
rotated 45.degree. (in plane) from the initial field direction. In
the end we obtained a thin film with polarization patterns showing
different transmittances to a polarized light. FIG. 4, panels b-d,
displays the POM images of as-prepared samples after the
application of different patterns. In these cases, the transmission
axis of the polarizer was set to be parallel to the initial field
direction. The areas cured during the first exposure appear dark
under the POM, owing to the parallel arrangement of the nanorods
relative to the transmission axis of the polarizer, while the areas
cured during the second exposure are bright since all nanorods are
oriented 45.degree. relative to the transmission axis of the
polarizer. An enlarged bright field optical microscopy image is
shown in FIG. 4, panel e, which accentuates the alignment of the
nanorods at the boundary of the bright (left) and dark (right)
areas (separated by the dotted line), and clearly confirms the
45.degree. angle between the two orientations.
[0136] Changing the orientation of the nanorods relative to the
transmission axis of the polarizer allows convenient modulation of
the transmittance intensity. As depicted in the extreme cases in
FIG. 5, panels a-d, shifting the transmission axis of the polarizer
to be parallel to the direction of the second field completely
reverses the dark and bright areas, while almost no contrast can be
observed under their bright-field optical images (FIG. 5, panels e
and f). In FIG. 5, panel g, we have plotted the dependence of
measured transmittance on the angle between the orientation of the
nanorods and the transmission axis of the polarizer, which is in
accordance with Equation 1. The transmittance of the polarized
light of the film or consequently its brightness under POM can be
fully modulated by controlling the relative orientation of the
nanorods in different areas during the lithographic processes. FIG.
5, panel h, demonstrates a single film with varying brightness in
different areas fabricated by a multi-step lithography process, in
which the magnetic field was gradually shifted from 0.degree. to
45.degree. relative to the transmission axis of the polarizer. The
polarization dependent transmittance of the pattern may be
immediately applicable in anti-counterfeiting devices.
Interestingly, if we only perform the first curing process, the
uncured areas remain in the liquid phase so that the orientation of
the nanorods within can still be tuned by magnetic fields, allowing
continuous change in the contrast between the pattern and the
background.
[0137] Depending on the direction of the applied external field,
the liquid crystals alter the polarization of light and are thus
able to control the intensity of the light transmitted through
them. Optical switching tests indicate that this liquid crystal is
extremely sensitive to the directional change of external magnetic
fields and exhibits an instant response within 0.01 s. The magnetic
nanorods can also be dispersed in a UV curable resin to produce
thin film liquid crystals, the orientation of which can be fixed
completely or in selected areas by combining magnetic alignment and
lithography processes, allowing the creation of patterns of
different polarizations and control over the transmittance of light
in particular areas.
[0138] The magnetically actuated liquid crystal is expected to
provide a new platform for fabricating novel optical devices that
can be widely applied in many fields, such as displays, waveguides,
actuators, optical modulators, and anti-counterfeiting
features.
Experimental
[0139] Synthesis of FeOOH Nanorods:
[0140] The synthesis of FeOOH nanorods is based on a previous
report with small modifications. Typically, 7.776 g of anhydrous
FeCl.sub.3 were dissolved in 80 mL water. The solution was added
into 450 .mu.L of 37% HC1 and then centrifuged at 11000 rpm for 3
min for the removal of unsolvable precipitates. The purified
solution was heated to 98.degree. C. in a 100 mL three-neck flask
with refluxing and was then maintained for 16 hrs. The solid
product was collected by centrifugation after the reaction and
washed by water for several times.
[0141] Silica Coating of FeOOH Nanorods:
[0142] 30 mg of as-prepared FeOOH nanorods was dispersed in 20 ml
of water, and 1 mL 0.1M PAA solution was added for the surface
modification of nanorods. After overnight stirring, the nanorods
were recovered by centrifugation and were redispersed in 3 mL
H.sub.2O. 1 mL of ammonia solution was then added, followed by the
addition of 20 mL ethanol and 100 .mu.L of TEOS. After 1 hr, the
silica-coated nanorods were collected by centrifugation, washed by
water for several times and redispersed in 2 mL of water.
[0143] Conversion of FeOOH@SiO.sub.2 Nanorods to
Fe.sub.2O.sub.4SiO.sub.2 Nanorods:
[0144] With the protection of nitrogen, 60 mL of diethylene glycol
was heated to 220.degree. C., to which 2 mL of FeOOH@SiO.sub.2
dispersion was added. The color of the mixture changes from yellow
to brownish, and finally black. The conversion usually takes 24
hrs, after which magnetic nanorods were collected by
centrifugation, washed by ethanol for several times and dispersed
in 5 mL of water.
[0145] Assembling Fe.sub.3O.sub.4SiO.sub.2 Nanorods into Liquid
Crystal:
[0146] As-reduced Fe.sub.3O.sub.4@SiO.sub.2 nanorods were further
purified by magnetic separation for three times. Then they were
concentrated to a volumetric fraction of 10% to allow the formation
of liquid crystal. Dispersions with different volumetric fractions
were also prepared by the same procedure.
[0147] Photopolymerization of Liquid Crystal:
[0148] A mixture solution of 7:3 polyethylene glycol diacrylate
(PEGDA, Mn: 700) to water was prepared. As-reduced
Fe.sub.3O.sub.4@SiO.sub.2 nanorods were dispersed in the mixture
solution and purified by magnetic separation for three times. The
solution was then concentrated to a volumetric fraction of 10%.
Photoinitiator was added into the solution at a mass fraction of
5%. For the photopolymerization, each time 5 .mu.L of solution was
used, sandwiched between one cover glass and one glass slide, and
then exposed under uv-light for 20 seconds.
[0149] It is understood that the examples and embodiments described
herein are for illustrative purposes only and that various
modifications or changes in light thereof will be suggested to
persons skilled in the art and are to be included within the spirit
and purview of this application and scope of the appended claims.
All publications, patents, and patent applications cited herein are
hereby incorporated by reference in their entirety for all
purposes.
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