U.S. patent application number 16/756809 was filed with the patent office on 2020-07-30 for aligned nematic elastomer.
The applicant listed for this patent is University of Leeds. Invention is credited to Helen Frances Gleeson, Devesh Arvind Mistry.
Application Number | 20200239774 16/756809 |
Document ID | 20200239774 / US20200239774 |
Family ID | 60481580 |
Filed Date | 2020-07-30 |
Patent Application | download [pdf] |
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United States Patent
Application |
20200239774 |
Kind Code |
A1 |
Gleeson; Helen Frances ; et
al. |
July 30, 2020 |
ALIGNED NEMATIC ELASTOMER
Abstract
There is provided the use of an aligned nematic elastomer to
form a material having auxetic properties wherein the aligned
nematic material has a mechanical Freedericksz transition. Also
provided is a method of producing an aligned nematic elastomer for
said use.
Inventors: |
Gleeson; Helen Frances;
(Leeds, West Yorkshire, GB) ; Mistry; Devesh Arvind;
(Leeds, West Yorkshire, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
University of Leeds |
Leeds |
|
GB |
|
|
Family ID: |
60481580 |
Appl. No.: |
16/756809 |
Filed: |
October 18, 2018 |
PCT Filed: |
October 18, 2018 |
PCT NO: |
PCT/GB2018/053018 |
371 Date: |
April 16, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09K 2019/0448 20130101;
C09K 19/12 20130101; C09K 2019/3004 20130101; C09K 19/3003
20130101; C09K 2019/548 20130101; C09K 2019/122 20130101; C09K
19/542 20130101; C09K 19/54 20130101; C09K 2019/3009 20130101 |
International
Class: |
C09K 19/12 20060101
C09K019/12; C09K 19/30 20060101 C09K019/30; C09K 19/54 20060101
C09K019/54 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 19, 2017 |
GB |
1717174.5 |
Claims
1. A method of producing a material having auxetic properties, said
method comprising the steps of: a) providing an aligned nematic
elastomer; and b) forming an aligned nematic material using the
aligned nematic elastomer, wherein the aligned nematic material has
a mechanical Freedericksz transition, thereby producing a material
having auxetic properties.
2. The method according to claim 1 wherein the auxetic properties
enable the material to be used in a medical device or in a
biomedical application.
3. The method according to claim 1 wherein the auxetic properties
enable the material to be used in a piezoelectric sensor or
actuator, or in a micro- or nano-mechanical or electromechanical
device.
4. The method according to claim 1 wherein the auxetic properties
enable the material to be used in composite materials as
reinforcements, or in personal protection clothing.
5. The method according to claim 1 wherein the aligned nematic
elastomer comprises a monodomain liquid crystal elastomer.
6. The method according to claim 5 wherein the monodomain liquid
crystal elastomer comprises; a polymeric component; a liquid
crystal mesogen component; and a cross-linker component, wherein
the liquid crystal mesogen component is physically linked to the
polymeric component.
7. The method according to claim 6 wherein the liquid crystal
mesogen component comprises a liquid crystal core component
selected from the group consisting of aromatic rings, aliphatic
rings, poly aromatic rings, poly aliphatic rings, phenyls,
biphenyls, benzenes, and combinations thereof.
8. The method according to claim 7 wherein the liquid crystal core
component is selected from one or more of the following systems:
##STR00003## wherein R and R' are independently selected from the
group consisting of alkyl, alkoxy, halide, --NO.sub.2 or --CN and
wherein the alkyl and alkoxy groups may be bivalent when forming
part of the linking group which connects the liquid crystal core
component to the polymeric component; and X and Y are independently
selected from the group consisting of --CH.dbd.CH--, --C.ident.--,
--CH.dbd.N--, --N.dbd.N--, or --C(O)O--.
9. The method according to claim 6 wherein the polymeric component
is formed from both mesogenic and non-mesogenic components.
10. The method according to claim 9 wherein the polymeric component
comprises an acrylate polymer and the non-mesogenic component
comprises 2-ethylhexyl acrylate.
11. The method according to claim 6 wherein the crosslinker
component comprises a mesogenic component.
12. The method according to claim 9 wherein the mesogenic component
is 6-(4-cyano-biphenyl-4'-yloxy)hexyl acrylate, the crosslinker
component is
1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene, and
the non-mesogenic component is 2-ethylhexyl acrylate.
13. A method of producing an aligned nematic elastomer, said method
comprising the steps of: a) applying an aligning means to a
substrate b) applying liquid crystal elastomer components to the
substrate and allowing them to form an aligned nematic phase c)
curing the liquid crystal elastomer components to form an aligned
nematic elastomer.
14. The method according to claim 13 wherein the aligning means is
an aligning force which is applied by brushing the substrate.
Description
[0001] The present invention relates to the use of an aligned
nematic elastomer, in particular to its use in forming material
having auxetic properties.
[0002] In conventional materials, when the material is stretched,
the material simultaneously becomes thinner in cross-section.
Similarly, if a conventional material is compressed, the material
expands laterally. These conventionally behaved materials have a
positive Poisson's ratio where the Poisson's ratio is described as
the negative ratio of the proportional decrease in a lateral
measurement to the proportional increase in length in a sample of
material that is elastically stretched. Materials with auxetic
properties on the other hand have a negative Poisson's ratio. On
stretching, the materials become thicker in one or both of the
directions perpendicular to the applied force. Auxetic materials
are of particular interest because of this unusual behaviour under
deformation. Auxetic materials exist in nature, for example some
minerals and a large number of cubic elemental metals, but
synthetic auxetic materials were only developed in the 1980s.
Macroscopic auxetic behaviour has been used in multiple
applications from sportswear to space travel. The design and
synthesis of molecular auxetic materials is a particularly exciting
prospect. However synthetic molecular auxetic materials have not
yet been developed.
[0003] Liquid crystals have long range order and through varying
the components that give the liquid crystals their desired
properties, the physical properties of the resulting materials can
be fine-tuned. It has therefore been suggested that liquid crystal
polymers may be developed which display auxetic properties.
However, to date no such material has been reported.
[0004] The applicant has surprisingly developed a self assembled
nematic material having auxetic properties.
[0005] In a first embodiment there is provided the use of an
aligned nematic elastomer to form a material having auxetic
properties wherein the aligned nematic material has a mechanical
Freedericksz transition (MFT).
[0006] It has surprisingly been found that by forming an aligned
nematic elastomer which displays an MFT the resulting material has
auxetic properties and therefore has use in a wide range of novel
applications. Because the materials have auxetic properties, they
demonstrate improved shock absorbance and shear performance. These
properties are useful in multiple applications. For example in
aerospace, automotive, defence and sports applications as well as
in biomedical fields where materials having auxetic properties can
be used to mimic biological systems. Use in medical devices such as
stents and valves and blood vessel dilators, where controlled
expansions and contraction using external stimuli are important, is
envisaged, as well as in prosthetic materials and surgical implants
where reaction to external pressures is of particular use. The
materials may also find use in medical attachment means such as
sutures and anchors or for controlled release of active
pharmaceutical ingredients through controlled contraction or
expansion.
[0007] Materials displaying auxetic properties may also find
application in piezoelectric sensors and actuators, as well as in
micro- and nano-mechanical and electromechanical devices. Other
potential uses include in composite materials where the materials
displaying auxetic properties could act as reinforcements, or in
personal protection clothing such as crash helmets, body armour,
and sports clothing where expansion in response to external forces
is clearly desirable.
[0008] A mechanical Freedericksz transition is defined as a
deformation mode of an aligned elastomer wherein the director
within the elastomer rotates sharply at a critical strain to
reorient towards the direction parallel to the stress axis at a
critical extension. Materials displaying this property were first
described by Mitchell et al (Mitchell, G. R., Davis, F. J. and Guo,
W., Phys. Rev. Lett., 1993, 71(18), 2947) and Roberts et al
(Roberts, P. M. S., Mitchell, G. R and Davis, F. J., J. Phys, II
France, 1997, 7, 1337 and Roberts, P. M. S., Mitchell, G. R, Davis,
F. J. and Pople, J. A., Mol. Cryst. Liq. Cryst., 1997, 299, 181).
An MFT is often described in analogy to the well-known electric (or
magnetic) field Freedericksz transitions (EFT) that occur in low
molar mass nematic display devices. In the EFT, the director
reorients sharply beyond a well-defined critical field (or
voltage), becoming increasingly aligned with respect to the
electric field as the amplitude of the field is increased. The EFT
threshold is discontinuous in theory, but is known to be softened
if an ideal LC monodomain with alignment exactly parallel or
perpendicular to the substrates is not achieved in practice. The
threshold is nonetheless sharp and well-defined. The sharp rotation
of the director seen in an MFT is different from the director
rotation response for an aligned elastomer which deforms via
semi-soft elasticity (SSE), the alternative deformation mode. In
the case of semi-soft elasticity, the director rotates
comparatively gradually over a plateau-like region of the tensile
load curve. A theoretical plot demonstrating an SSE transition is
shown in FIG. 1. The director rotates gradually across region
II.
[0009] The mechanical Freedericksz transition is measurable by
applying stress in a direction perpendicular or close to
perpendicular to the aligned director in a sample and tracking the
orientation of the director, for example by using polarising
microscopy.
[0010] Such a method comprises: [0011] loading a strip of the
elastomer into clamps of opposing actuators, placing the strip
between crossed polarisers; [0012] applying strain incrementally by
imposing extension steps of 5% of the strip's initial length per
minute, in a direction perpendicular to the initial director
orientation; [0013] at each extension increment, taking a series of
measurements of transmitted light intensity (intensity of light
transmitted through the polariser, strip and analyser), with the
polariser and analyser being rotated relative to the strip by 10
degrees between each measurement. [0014] fitting the measurements
of transmitted intensity using equation
[0014] I = I 0 sin 2 ( b .pi. .times. ( .theta. - c ) 1 8 0 ) + d
##EQU00001##
to determine c, the angle of the director relative to the direction
of the applied stress (where I is the measured intensity, .theta.
is the angle between the polariser and the fast axis of the
birefringent material projected onto the plane of the polarizer,
and I.sub.0, b, c, and d are fitting parameters). [0015] from the
relationship between the director angle and the extension ratio,
the critical extension ratio at which the elastomer undergoes the
MFT can be determined--at the critical extension ratio, the
director sharply rotates.
[0016] The aligned nematic elastomer preferably comprises a
monodomain liquid crystal elastomer. More preferably the aligned
nematic elastomer is a monodomain liquid crystal elastomer.
[0017] By "monodomain" herein is meant that the director
orientation of the elastomer is macroscopically aligned in the
sample. Monodomain alignment over the sample can be determined, for
example, by polarising microscopy where it is characterised by
uniform birefringence when the macroscopic sample is viewed between
crossed polarisers.
[0018] Preferably the aligned nematic elastomer comprises a
monodomain liquid crystal elastomer comprising; a polymeric
component; a liquid crystal mesogen component; and a cross-linker
component, wherein the liquid crystal mesogen component is
physically linked to the polymeric component.
[0019] Preferably the liquid crystal mesogen component is
physically linked to the polymeric component via a flexible
spacer.
[0020] Preferably the flexible spacer comprises a C.sub.2-C.sub.10
alkylene group, preferably a linear C.sub.2-C.sub.10 alkylene
group, more preferably a linear C.sub.3-C.sub.7 alkylene group,
most preferably a linear C.sub.3 or C.sub.6 alkylene group. For
example, the flexible spacer may comprise an ethylene, propylene,
butylene, pentylene, hexylene, heptylene, octylene, nonylene or
decylene group.
[0021] The liquid crystal mesogen component of the liquid crystal
elastomer may comprise any suitable nematic mesogen.
[0022] Preferably the liquid crystal mesogen component comprises a
liquid crystal core component selected from the group consisting of
aromatic rings, aliphatic rings, poly aromatic rings, poly
aliphatic rings, phenyls, biphenyls, benzenes, and combinations
thereof.
[0023] Preferably the liquid crystal core component comprises a
plurality of aromatic and/or aliphatic rings.
[0024] Preferably the liquid crystal core component is selected
from one or more of the following systems:
##STR00001##
wherein R and R' are each independently selected from the group
consisting of alkyl, alkoxy, halide, --NO.sub.2 or CN and wherein
the alkyl and alkoxy groups may be bivalent when forming part of
the linking group which connects the liquid crystal core to the
polymeric component; and X and Y are each independently selected
from the group consisting of CH.dbd.CH, --C.ident.C--,
--CH.dbd.N--, --N.dbd.N--, or --C(O)O--.
[0025] Preferably the liquid core component comprises at least two
phenyl groups.
[0026] The phenyl groups may be optionally substituted with any
suitable functional group.
[0027] Preferably at least one of X or Y is --C(O)O-- or X or Y is
absent.
[0028] Preferably the liquid crystal core component is selected
from a 4-cyano-biphenyl-4'-yloxy, a 4-oxyphenyl 4-methoxybenzoate
or a 4-oxyphenyl 4-(trans-4-propylcyclohexyl)benzoate group.
[0029] In certain embodiments the liquid crystal mesogen component
is present as part of the side chain of the polymeric component,
i.e. the liquid crystal mesogen component is a pendant group
extending from the backbone of the polymeric component.
[0030] In certain embodiments the liquid crystal mesogen component
is present as part of the backbone of the polymeric component.
[0031] The liquid crystal mesogen component may form part of both
the side chain and backbone of the polymeric component.
[0032] The cross-linker component preferably comprises a
bifunctional monomer having the same functionality as the polymeric
component.
[0033] Preferably the cross-linker component also comprises a
mesogenic component. Preferably the mesogenic component comprises a
liquid crystal core component selected from one or more of the
following systems:
##STR00002##
wherein R and R' are each independently selected from the group
consisting of alkyl, alkoxy, halide, --NO.sub.2 or --CN and wherein
the alkyl and alkoxy groups may be bivalent when forming part of
the linking group which connects the liquid crystal core to the
polymeric component; and X and Y are each independently selected
from --CH.dbd.CH--, --C.ident.C--, --CH.dbd.N--, --N.dbd.N--, or
--C(O)O--.
[0034] Preferably the liquid core component comprises at least
three phenyl groups. Preferably at least one of X or Y is
--C(O)O--.
[0035] The phenyl groups may be optionally substituted with any
suitable functional group. Preferably the phenyl groups are
optionally substituted with one or more C1-C3 alkyl groups, most
preferably with one or more methyl groups.
[0036] Preferably the liquid core component comprises an optionally
substituted bis-oxybenzoyloxybenzene group. Most preferably a
bis-oxybenzoyloxy-2-methylbenzene group
[0037] The polymeric component may be any suitable polymeric
component. Preferably the polymeric component comprises an acrylate
polymer, a vinyl polymer, a siloxane polymer, a thiol based
polymer, an amine based polymer or an epoxide based polymer. Most
preferably the polymeric component comprises an acrylate
polymer.
[0038] In certain embodiments the polymeric component is formed
from both mesogenic and non-mesogenic components.
[0039] Preferably the mesogenic components are formed from
mesogenic monomers which comprise a monomer unit linked to a liquid
crystal core component.
[0040] The non-mesogenic component may be a Tg reducing component.
In preferred embodiments the elastomer for use according to the
first embodiment of the invention has a Tg at or below room
temperature (25.degree. C.).
[0041] In preferred embodiments the Tg reducing components may be
formed from monomers which comprise a monomer unit and a pendant
medium chain (C.sub.2-C.sub.12) straight or branched alkyl
group.
[0042] In particularly preferred embodiments the polymeric
component comprises an acrylate polymer and the Tg reducing
component comprises ethyl hexyl acrylate.
[0043] In preferred embodiments of the invention, the polymeric
component comprises a polyacrylate, the liquid crystal core
component is a 4-cyano-biphenyl-4'-yloxy component and the
crosslinker component comprises a bis-oxybenzoyloxy-2methylbenzene
comprising component.
[0044] The elastomer for use according to the first embodiment is
preferably formed by polymerising a mixture comprising a mesogenic
monomer, a crosslinking component and an initiator. The mixture may
further comprise a non-mesogenic monomer to modify the properties
of the final elastomer, for example to lower the Tg of the final
elastomer. The mixture may also further comprise a non-reactive
mesogenic component to broaden the nematic phase range prior to
polymerisation. In preferred embodiments the crosslinking component
also comprises a mesogenic component.
[0045] Preferably the mesogenic monomer comprises about 5-50% by
mol. of the monomer mixture prior to polymerisation, more
preferably about 10-30% by mol., most preferably approximately 15%
by mol. In the final elastomer, the proportion of the material
derived from the mesogenic monomer is preferably about 20-70% by
mol., most preferably about 30-60% by mol.
[0046] Preferably the crosslinker component comprises about 1-20%
by mol. of the monomer mixture prior to polymerisation, more
preferably about 3-10% by mol, most preferably about 3-8% by mol.
In the final elastomer, the proportion of the material derived from
the crosslinker component is preferably about 5-20% by mol., most
preferably about 8-17% by mol.
[0047] Preferably at least 10% of the crosslinker component
comprises a mesogenic component, preferably at least 20%, at least
30%, at least 40%, at least 50%, at least 60%, at least 70%, at
least 80%, at least 90% or at least 95% of the crosslinker
component comprises a mesogenic component.
[0048] The initiator chosen will be dependent on the polymer used
and may be any suitable initiator. However, when the polymer is a
polyacrylate the initiator is preferably a photoinitiator. Possible
photoinitiators are well known to those skilled in the art and
include benzoin ethers, benzyl ketals, alpha-dialkoxyacetophenones,
alpha-hydroxyalkylphenones, acylphosphine oxides, benzophenones and
thioxanthones. Preferably the photoinitiator is methyl
benzoylformate. Preferably the initiator is present in an amount of
approximately 1.5% by mol. of the monomer mixture.
[0049] When a non-mesogenic monomer is present in the monomer
mixture, the non-mesogenic mixture preferably comprises about
10-40% by mol. of the monomer mixture, more preferably about 15-30%
by mol., most preferably about 15-20% by mol. In the final
elastomer, the proportion of the material derived from the
non-mesogenic monomer, if present, is preferably about 20-60% by
mol, most preferably about 35-50% by mol.
[0050] When a non-reactive mesogen is present in the monomer
mixture, the non-reactive mesogen preferably comprises about 10-70%
by mol. of the monomer mixture, more preferably about 20-60% by
mol., or 30-60% by mol., most preferably approximately 55% by mol.
In preferred embodiments the non-reactive mesogen is
4-cyano-4'-hexyloxybiphenyl.
[0051] In preferred embodiments, the mesogenic monomer is
6-(4-cyano-biphenyl-4'-yloxy)hexyl acrylate, 4-methoxybenzoic acid
4-(6-acryloyloxy-hexyloxy)phenyl ester or
4-{6-(acryloyloxy)hexyloxy}phenyl
4-(trans-4-propylcyclohexyl)benzoate, the crosslinker component is
1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene or
1,4-bis-[4-(3-acryloyloxypropyloxy)benzoyloxy]-2-methylbenzene, the
non-mesogenic monomer is 2-ethylhexyl acrylate and, if present, the
non-reactive mesogen is 4-cyano-4'-hexyloxybiphenyl.
[0052] In preferred embodiments, the mesogenic monomer is
6-(4-cyano-biphenyl-4'-yloxy)hexyl acrylate, the crosslinker
component is
1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene, the
non-mesogenic monomer is 2-ethylhexyl acrylate and, if present, the
non-reactive mesogen is 4-cyano-4'-hexyloxybiphenyl; or the
mesogenic monomers are 4-methoxybenzoic acid
4-(6-acryloyloxy-hexyloxy)phenyl ester and
4-{6-(acryloyloxy)hexyloxy}phenyl
4-(trans-4-propylcyclohexyl)benzoate, the crosslinker component is
1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene the
non-mesogenic monomer is 2-ethylhexyl acrylate and, if present, the
non-reactive mesogen is 4-cyano-4'-hexyloxybipheny; or the
mesogenic monomers are 4-methoxybenzoic acid
4-(6-acryloyloxy-hexyloxy)phenyl ester and
4-{6-(acryloyloxy)hexyloxy}phenyl
4-(trans-4-propylcyclohexyl)benzoate, the crosslinker component is,
4-bis-[4-(3-acryloyloxypropyloxy)benzoyloxy]-2-methylbenzene, the
non-mesogenic monomer is 2-ethylhexyl acrylate and, if present, the
non-reactive mesogen is 4-cyano-4'-hexyloxybiphenyl.
[0053] According to a further embodiment of the invention is
provided a method of producing an aligned nematic elastomer for use
according to the first embodiment of the invention, said method
comprising the steps of: [0054] a) applying an aligning means to a
substrate [0055] b) applying the liquid crystal elastomer
components to the substrate and allowing them to form an aligned
nematic phase [0056] c) curing the liquid crystal elastomer
components to form an aligned nematic elastomer.
[0057] Various techniques for aligning mesogenic compositions
exist. For example, techniques exist to create a monodomain during
synthesis, including applying a magnetic field, mechanical
brushing, flow, applying an electric field, applying a thermal
gradient, or providing an alignment layer or layers. The monomeric
solution may also be heated, cooled or exposed to other
environmental factors to influence synthesis of the monomer mixture
into an aligned state.
[0058] Preferably the aligning means is an aligning force which is
applied by brushing the substrate, preferably to impart a static
force to the substrate.
[0059] When the crosslinking component comprises a mesogenic
component and therefore may also be considered a mesogenic monomer,
the ratio of mesogenic monomers to non-mesogenic monomers in the
final elastomer is preferably between 2:1 and 1:1.
[0060] Embodiments of the invention will now be described with
reference to the accompanying examples and by reference to the
drawings in which:--
[0061] FIG. 1 shows a theoretical plot of extension ratio vs stress
for a material showing an SSE transition;
[0062] FIGS. 2a, 2b, 2c and 2d show plots of the fractional
thickness vs the extension ratio and the Poisson's ratio vs the
extension ratio of the materials of examples 1 to 4 respectively.
Sub-zero values of the Poisson's ratio indicate the auxetic
behaviour;
[0063] FIGS. 3a, 3b, 3c and 3d show plots of the tensile load
curves and director angle response vs extension ratio for materials
of examples 1 to 4 respectively; and
[0064] FIG. 4 shows a plot of the fractional change vs strain for
the material of example 1 at varying temperature and varying
extension rate.
EXAMPLES
[0065] Elastomer Synthesis
[0066] Aligned nematic elastomers for use according to the
invention were synthesised as follows using the following
materials: [0067] 2-ethylhexyl acrylate (EHA), [0068]
6-(4-cyano-biphenyl-4'-yloxy)hexyl acrylate (A6OCB), [0069]
4-methoxybenzoic acid 4-(6-acryloyloxy-hexyloxy)phenyl ester (M1)
[0070] 4-{6-(acryloyloxy)hexyloxy}phenyl
4-(trans-4-propylcyclohexyl)benzoate (M2) [0071]
1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene
(RM82), [0072]
1,4-bis-[4-(3-acryloyloxypropyloxy)benzoyloxy]-2-methylbenzene
(RM257) [0073] 4-cyano-4'-hexyloxybiphenyl (6OCB) and [0074] methyl
benzoylformate (MBF).
[0075] The elastomers for use according to the invention were
prepared using the following starting compositions:
TABLE-US-00001 Material % by mol Component Example 1 Example 2
Example 3 Example 4 A60CB 14.6 24.4 0 0 M1 0 0 15.5 15.3 M2 0 0 5.6
5.5 60CB 55.9 54.6 50.0 50.7 RM82 7.1 3.5 5.6 0 RM257 0 0 0 5.3 EHA
20.9 16.0 22.4 22.3 MBF 1.6 1.5 0.8 0.8
[0076] Using a balance with an accuracy of 0.3 mg, dry materials
were measured into a 4 ml sample vial. The mixture was then heated
to 100.degree. C. and stirred at 60 rpm for 5 minutes. The liquid
materials were added and the vial was placed on a separate stirring
plate held at 40.degree. C. and stirred at 60 rpm for a further 5
minutes.
[0077] The mixtures were then filled in the isotopic phase at
40.degree. C. into the cells previously prepared via capillary
action and left for approximately half an hour to cool to ambient
temperature allowing the nematic phase to form via alignment with
the rubbing direction. Once aligned, the cells were placed under a
low intensity UV fluorescence light source (intensity of 2.5 mW
cm.sup.-2) for two hours to cure. Once separated from the cells,
the film was washed in dicholoromethane (DCM) by slowly adding DCM
stepwise to about 30% concentration. Solvents were exchanged
several times to ensure all waste materials were removed before
deswelling the LCE films by adding methanol stepwise. The films
were left to dry fully overnight before testing.
[0078] The auxetic properties of the four materials are
demonstrated in FIGS. 2a, 2b, 2c and 2d respectively which show the
materials to have a negative Poisson's ratio. Beyond an extension
ratio of approximately 1.8 in FIG. 2a, approximately 1.5 in FIG.
2b, approximately 1.6 in FIG. 2c and approximately 1.6 in FIG. 2d,
the fractional thickness of the materials increases with increasing
extension ratio. FIGS. 3a, 3b, 3c and 3d demonstrate that the
materials each possess an MFT. In FIG. 3a a sharp change in
director angle is seen at a strain of approximately 2.1. In FIG. 3b
a sharp change in director angle is seen at an x deformation of
approximately 1.9. In FIG. 3c a sharp change in director angle is
seen at an x deformation of approximately 1.9. In FIG. 3d a sharp
change in director angle is seen at an x deformation of
approximately 1.9.
* * * * *