U.S. patent application number 13/284061 was filed with the patent office on 2012-05-03 for nanotube film electrode and an electroactive device fabricated with the nanotube film electrode and methods for making same.
This patent application is currently assigned to U.S.A. as represented by the Administrator of the National Aeronautics and Space Administration. Invention is credited to Joycelyn S. Harrison, Jin Ho Kang, Cheol Park.
Application Number | 20120107594 13/284061 |
Document ID | / |
Family ID | 39468603 |
Filed Date | 2012-05-03 |
United States Patent
Application |
20120107594 |
Kind Code |
A1 |
Kang; Jin Ho ; et
al. |
May 3, 2012 |
Nanotube Film Electrode and an Electroactive Device Fabricated with
the Nanotube Film Electrode and Methods for Making Same
Abstract
Disclosed is a single wall carbon nanotube (SWCNT) film
electrode (FE), all-organic electroactive device systems fabricated
with the SWNT-FE, and methods for making same. The SWCNT can be
replaced by other types of nanotubes. The SWCNT film can be
obtained by filtering SWCNT solution onto the surface of an
anodized alumina membrane. A freestanding flexible SWCNT film can
be collected by breaking up this brittle membrane. The conductivity
of this SWCNT film can advantageously be higher than 280 S/cm. An
electroactive polymer (EAP) actuator layered with the SWNT-FE shows
a higher electric field-induced strain than an EAP layered with
metal electrodes because the flexible SWNT-FE relieves the
restraint of the displacement of the polymeric active layer as
compared to the metal electrode. In addition, if thin enough, the
SWNT-FE is transparent in the visible light range, thus making it
suitable for use in actuators used in optical devices.
Inventors: |
Kang; Jin Ho; (Newport News,
VA) ; Park; Cheol; (Yorktown, VA) ; Harrison;
Joycelyn S.; (Arlington, VA) |
Assignee: |
U.S.A. as represented by the
Administrator of the National Aeronautics and Space
Administration
Washington
DC
|
Family ID: |
39468603 |
Appl. No.: |
13/284061 |
Filed: |
October 28, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11937155 |
Nov 8, 2007 |
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13284061 |
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60857531 |
Nov 8, 2006 |
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60984027 |
Oct 31, 2007 |
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Current U.S.
Class: |
428/220 ;
156/249; 156/306.3; 156/308.2; 423/276; 423/290; 423/298;
423/447.2; 428/221; 977/750; 977/751; 977/752; 977/762;
977/832 |
Current CPC
Class: |
B32B 37/10 20130101;
B32B 37/06 20130101; B32B 2457/00 20130101; B32B 2313/04 20130101;
H01L 41/0478 20130101; B32B 43/006 20130101; B32B 37/14 20130101;
H01L 41/45 20130101; B32B 5/16 20130101; H01B 1/04 20130101; B32B
2315/02 20130101; H01L 41/29 20130101; Y10T 156/10 20150115; Y10S
977/752 20130101; B82Y 30/00 20130101; B32B 2250/02 20130101; B32B
2313/02 20130101; Y10S 977/751 20130101; Y10S 977/762 20130101;
B32B 2264/108 20130101; Y10S 977/75 20130101; C08K 7/24 20130101;
B32B 2309/12 20130101; Y10T 428/249921 20150401 |
Class at
Publication: |
428/220 ;
423/447.2; 423/298; 423/276; 423/290; 156/306.3; 156/308.2;
156/249; 428/221; 977/750; 977/752; 977/751; 977/832; 977/762 |
International
Class: |
D01F 9/12 20060101
D01F009/12; C01B 21/082 20060101 C01B021/082; C01B 21/064 20060101
C01B021/064; B32B 37/06 20060101 B32B037/06; B32B 38/10 20060101
B32B038/10; B32B 5/16 20060101 B32B005/16; C01B 35/02 20060101
C01B035/02; B32B 37/10 20060101 B32B037/10 |
Goverment Interests
ORIGIN OF THE INVENTION
[0002] The invention described herein was made by an employee of
the United States Government and may be manufactured and used by or
for the Government of the United States of America for governmental
purposes without the payment of any royalties thereon or therefor.
Claims
1. A film electrode consisting of an electrically conductive
nanotube film consisting essentially of a plurality of
interpenetrated nanotubes, wherein the thickness of the film is
configured to achieve a desired compliance required for a specific
application.
2. The film electrode of claim 1, wherein the desired compliance is
the same as, or similar to, the compliance of an active layer to be
used with said electrode.
3. The film electrode of claim 1, wherein said film thickness is
determined by adjusting the concentration and quantity of said
interpenetrated carbon nanotubes so as to achieve a desired
density
4. The film electrode of claim 1, wherein said plurality of
interpenetrated nanotubes comprise at least one of: single-walled
carbon nanotubes; multi-walled carbon nanotubes; few walled carbon
nanotubes; boron nanotubes; boron carbon nitride nanotubes, and
boron nitride nanotubes.
5. The film electrode of claim 1, wherein said film is configured
to have a conductivity o a least about 280 S/cm.
6. The film electrode of claim 1, wherein said electrode is capable
of operating in applications of up to about 400.degree. C.
7. The film electrode of claim 1, wherein said thickness ranges
from about several tens of nanometers to about several hundreds of
micrometers.
8. An electroactive device fabricated with a nanotube film
electrode, comprising: at least one nanotube film electrode; and at
least one active layer; wherein each of said at least one nanotube
film electrode has a compliance substantially matching the
compliance of said at least one active layer.
9. The electroactive device of claim 8, wherein said active layer
comprises an electroactive polymer.
10. The electroactive device of claim 8, wherein the compliance of
said at least one nanotube film electrode is controlled at least in
part by its density.
11. The electroactive device of claim 8, wherein said device is
capable of functioning in high temperature applications of at least
up to about 220.degree. C.
12. The electroactive device of claim 8, wherein at least two
nanotube film electrodes are present for each active layer, and
each active layer has one film electrode on a top surface and one
film electrode on a bottom surface.
13. The electroactive device of claim 8, wherein said nanotube film
electrode consists essentially of at least one or more of:
single-walled carbon nanotubes; multi-walled carbon nanotubes; few
walled carbon nanotubes; boron nanotubes; boron carbon nitride
nanotubes, and boron nitride nanotubes.
14. A method for making an electroactive device having a nanotube
film electrode comprising the steps of: providing at least one
nanotube film electrode; providing at least one active layer;
placing said at least one nanotube film electrode in contact with
said at least one active layer; applying sufficient pressure to
said at least one nanotube film electrode and said at least one
active layer so as to produce an electroactive device having a
substantially uniform compliance throughout.
15. The method of claim 14, comprising the step of heating said at
least one nanotube film electrode and said at least one active
layer.
16. The method of claim 14, wherein said sufficient pressure ranges
between about 600 to about 6000 psi.
17. The method of claim 14, wherein said step of applying
sufficient pressure comprises utilizing silicone elastomer plates
on press plates.
18. The method of claim 14, where said active layer comprises an
electroactive polymer.
19. The method of claim 14, wherein the nanotube film electrode
consists essentially of at east one or more of: single-walled
carbon nanotubes; multi-walled carbon nanotubes; few walled carbon
nanotubes; boron nanotubes; boron carbon nitride nanotubes, and
boron nitride nanotubes.
20. The method of claim 14, wherein the nanotube film electrode is
prepared by a process comprising the steps of: dispersing
conductive nanotubes in a surfactant-free solvent under sonication
to form a solution; providing a breakable porous membrane;
filtering the solution onto the membrane; and delaminating the
nanotube film electrode from the membrane by physically breaking
the membrane.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This patent application is a divisional of copending U.S.
patent application Ser. No. 11/937,155, filed Nov. 8, 2007; this
application claims the benefits of U.S. Provisional Application
Nos. 60/857,531, tiled Nov. 8, 2006, and 60/984,027 filed Oct. 31,
2007; the contents of all of which are incorporated herein in their
entirety.
FIELD OF THE INVENTION
[0003] This invention relates generally to electroactive polymeric
devices and compliant electrodes for these devices. More
specifically, the invention relates to electroactive polymeric
devices utilizing highly compliant nanotube film electrodes and
methods for making same.
DESCRIPTION OF THE RELATED ART
[0004] As an interest in high performance polymeric electroactive
devices increases, a request for new electrode materials has
emerged. Known electroactive polymeric devices typically use metal
electrodes, such as silver and gold, to provide electric fields.
These metal electrodes often inhibit the displacement (elongation
or contraction) of their electroactive layer because of less
compliance (greater stiffness (modulus)) of the metal electrodes
than the active polymer itself. Thus, the actual electric
field-induced strain output of these devices with metal electrodes
is always smaller than what they could intrinsically provide.
[0005] Conducting polymers have been used as alternative electrodes
for electroactive polymeric devices. The conducting polymers
relieved the restraint of movement in the polymeric active layer
because their compliance is similar to that of the active polymeric
layer, and exhibited higher strain than metal electrodes did.
However, these conducting polymers have a disadvantage of low
conductivity at high temperatures because of dehydration phenomena
and dedoping, and therefore are unable to be used for applications
which require high thermal stability. Therefore, a need existed for
an alternative electrode with less stiffness than the conventional
metallic electrodes and with good thermal stability.
SUMMARY OF THE INVENTION
[0006] In accordance with at least one embodiment of the present
invention a novel freestanding flexible single-walled carbon
nanotubes (SWCNT) film electrode (SWCNT-FE) is provided. This
inventive electrode shows high conductivity and good thermal
stability with comparable compliance to polymeric active layers.
Additionally, in accordance with at least one embodiment of the
present invention, a novel high performance all-organic
electroactive device (or system) is provided, fabricated with the
SWCNT-FE. Methods for the preparation of the electrode and device
are also provided within the scope of the present invention.
Features and advantages of the inventions will be apparent from the
following detailed description taken in conjunction with the
following figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1A is a schematic diagram depicting the preparation of
an all-organic electroactive device system in accordance with at
least one embodiment of the present invention;
[0008] FIG. 1B shows a photograph of a prototype of a transparent
electroactive device fabricated with an LAP active layer and SWNT
film electrodes, in accordance with at least one embodiment of the
present invention;
[0009] FIG. 2A shows a cross-sectional SEM image of SWCNT-FE after
pressing at 600 psi, in accordance with at least one embodiment of
the present invention;
[0010] FIG. 2B shows a more detailed image of the pulled and porous
networked SWCNTs shown in FIG. 2A;
[0011] FIG. 2C shows a cross sectional SEM image of SWCNT-FE after
pressing at 6000 psi, in accordance with at least one embodiment of
the present invention;
[0012] FIG. 3A is a graph depicting the dielectric constant of an
inventive EAP layered with SWCNT-FE as a function of temperature
and frequency;
[0013] FIG. 3B is a graph depicting the dielectric constant of an
EAP layered with metal electrodes as a function of temperature and
frequency;
[0014] FIG. 4 is a graph depicting the electric field-induced
strain of an EAP layered with metal electrodes, and with an
inventive SWCNT-FE;
[0015] FIGS. 5A and 5B are photographs of a freestanding flexible
SWCNT-FE in accordance with at least one embodiment of the present
invention, after it is removed from the membrane (shown in 5B), in
accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Shown in the drawings and described herein in detail are
advantageous embodiments of the present invention. It should be
understood that the present invention is susceptible of embodiments
in many different forms and thus the present disclosure is to be
considered as an exemplification of the principles of the invention
and is not intended to limit the broad aspect of the invention to
the embodiments described and illustrated herein.
[0017] Referring now to the drawings, FIG. 1A is a diagram
depicting the preparation of an all-organic electroactive device
system in accordance with at least one embodiment of the present
invention (such as the device 10 shown in FIG. 1B). A SWCNT film
can be prepared by a method similar to the method set forth in A.
G. Rinzler and Z. Chen, U.S. Patent Application Publication
20040197546 (Oct. 7, 2004), the entire contents of which are hereby
incorporated by reference. However, in accordance with the present
invention, unlike U.S. Application Publication 20040197546, no
surfactant is required to develop the SWNT film and no solvent is
necessary to isolate the SWNT film from the filter membrane (by
dissolving the membrane). Additionally, it should be understood
that while the described inventive embodiment utilizes SWCNTs, it
is nevertheless within the scope of the present invention to
replace the SWCNTs with multi-walled carbon nanotubes (MWCNT) or
few wall carbon nanotubes (FWCNT). Additionally, other types of
conductive nanotubes can be used in the instant invention, for
example, boron nanotubes, boron carbon nitride nanotubes, and/or
boron nitride nanotubes.
[0018] To explain, in accordance with one inventive method, the
inventive electrode can be developed as follows. First, SWCNTs can
be dispersed in an solvent, such as N,N-Dimethylacetamide (DMAc),
under sonication and filtered onto the surface of a brittle or
breakable porous membrane, such as an anodized alumina membrane
(pore size: 0.2 .mu.m), to form a SWNT film on the membrane.
Advantageous dispersion methods (not requiring surfactants or
covalent bonds), and choices of appropriate solvents, which can be
utilized in accordance with the present invention, can be found in
co-pending U.S. Patent Applications, namely, application Ser. No.
10/288,797, entitled " Electrically Conductive, Optically
transparent Polymer/Carbon Nanotube Composites and Process for
Preparation Thereof," filed Nov. 1, 2002; application Ser. No.
11/432,201, entitled "Dispersions of Carbon Nanotubes in Polymer
Matrices," filed on May 11, 2006; and application Ser. No.
11/644,019, entitled "Nanocomposites from Stable Dispersions of
Carbon Nanotubes in Polymeric Matrices Using Dispersion
Interaction," filed on Dec. 22, 2006. These three pending U.S.
patent applications are incorporated herein by reference as set
forth in their entirety.
[0019] After the formation of the SWCNT film on the membrane (for
example, through the removal of the solvent in a known manner), a
freestanding SWCNT film can then be easily delaminated by breaking
the brittle (e.g. alumina) membrane. This breaking can be
accomplished in a manner that would be known to one skilled in the
art, the result of which is shown in FIG. 5B. In one advantageous
embodiment, the delaminated SWCNT film will have the conductivity
of about 280 S/cm. The thickness of the SWCNT film can be
controlled from several tens of nanometers to several hundreds of
micrometers by adjusting the concentration and quantity of SWCNT
solution used. Adjusting the concentration and quantity of SWCNT
solution used will also affect the final conductivity of the SWCNT
film. Additionally, adjusting the thickness of the film will affect
the transparency of the film. For example, it was found that a 2
.mu.m thick SWCNT film was opaque (black), while a 300 nm thick
SWCNT film was found to be optically transparent.
[0020] In accordance with at least one advantageous embodiment of
the present invention, as shown in FIG. 1A, an inventive
all-organic electroactive device (SWCNT-FE/EAP/SWCNT-FE) can be
fabricated with an electroactive polymer (EAP) active layer 11 and
the SWCNT films 12, 13 by pressing, for example, at 600, 3000 or
6000 psi, as shown in FIG. 1A. In accordance with one embodiment of
the invention, the pressing temperature and time were 230.degree.
C. and 2 min. respectively. All of the sample specimens were
preheated at 230.degree. C. for 20 minutes prior to pressing.
Silicone elastomer plates 14, 15 (e.g., 3 mm thick) can be used on
the press plate surfaces for better contact adhesion between the
SWCNT film and the actuating layer. This polymeric electroactive
device layered with the SWCNT-FE can serve as an actuator. However,
it should be understood that it is within the scope of the present
invention that other devices (such as sensors, transducers, etc.)
could also be fabricated utilizing the novel methods and inventions
set forth herein. Additionally, the embodiment shown in FIG. 1A is
merely illustrative of one possible device design. As is known in
the art, depending upon the desired application and geometry, the
device could be configured in many different ways, for example,
with different numbers, sizes, shapes and locations of active
layers and electrodes (e.g., round, interdigitated, etc.). Also,
different types of active layers could be utilized, depending upon
the application for which the particular device is designed.
Examples of various active layers can be found in U.S. Pat. Nos.
5,891,581 and 5,909,905, as well as pending U.S. patent application
Ser. No. 11/076,460, entitled "Sensing/Actuating Materials Made
from Carbon Nanotube Polymer Composites and Methods for Making
Same," filed Mar. 3, 2005, and pending U.S. patent application Ser.
No. 11/081,888, entitled, "Multilayer Electroactive Polymer
Composite Material," filed on Mar. 9, 2005. These patents and
applications are hereby incorporated by reference as if set forth
in their entirety herein
[0021] FIGS. 2A and 2C show SEM images of cross-sections of
inventive SWCNT-FEs 22, 23 after pressing at 600 psi and at 6000
psi, respectively. FIG. 2B shows a more detailed image of the
pulled and porous networked SWCNTs shown in FIG. 2A. The
cross-section of the SWCNT-FE 23 pressed under 6000 psi (FIG. 2C)
was denser than that pressed under 600 psi (FIG. 2A).
[0022] The density (modulus or compliance) of the SWNT-FE can be
controlled by adjusting the fabrication pressure. As explained more
fully below, it is anticipated that less dense (higher compliance)
SWCNT-FE can present less constraint to the displacement by more
closely matching the modulus of the polymeric active layers.
Therefore, in at least one advantageous embodiment of the present
invention, the fabrication pressure is adjusted to produce a
SWCNT-FE with a compliance (and modulus) substantially matching the
compliance of the device's active layer. In this manner a device
can be fabricated with substantially uniform compliance throughout,
thereby potentially improving the performance of the device, for
example, by maximizing the electric field-induced strain output of
the device.
[0023] Most conducting polymers become unstable above 120.degree.
C., and lose their conductivity significantly. However, for many
applications, the actuator system must be able to function at
temperatures even up to 200.degree. C. or higher. Therefore, it was
necessary to examine if SWCNT-FE functions at a broad range of
temperatures and frequencies. The performance of the SWCNT film as
an electrode was evaluated by measuring the dielectric properties
of an Electroactive Polymer (EAP) layered with the SWNT film as an
electrode (SWCNT-FE) at a broad range of temperatures (from
25.degree. C. to 280.degree. C.) and frequencies (from 1 KHz to 1
MHz). The temperature and frequency dependence of the dielectric
constant for an EAP layered with SWCNT-FE is shown in FIG. 3A,
which is almost the same as that of the dielectric properties of
the same EAP layered with gold electrodes (FIG. 3B). The dielectric
constant remained constant up to 220.degree. C., and then
increased. The increase of the dielectric constant at 220.degree.
C. is due to the glass transition temperature (T.sub.g) of the EAP
(.beta.-CN)APB/OPA polyimide, U.S. Pat. No. 5,891,581 Joycelyn O.
Simpson and Terry St. Clair, "Thermally stable, piezoelectric and
pyroelectric polymeric substrates"). Above T.sub.g, dipoles have a
higher mobility and show a higher dielectric constant.
Additionally, as frequency decreases, it is believed that these
dipoles have enough time to orient themselves under an applied
electric field, creating a higher dielectric constant. Thermally
stable dielectric properties suggest that SWCNT-FE is suitable for
high temperature applications at least up to 220.degree. C. SWCNT
usually do not oxidize below a temperature of about 400.degree. C.,
therefore, if a higher stability polymer was used a fabricated
device could potentially function at a much higher temperature.
Success in the use of known conducting polymer electrodes at high
temperatures (above 100.degree. C.) has rarely been reported.
Conducting polymers have a disadvantage of low conductivity at high
temperatures because of dehydration phenomena and dedoping, and
therefore are unable to be used for applications which require high
thermal stability.
[0024] Electric field-induced strain values for EAP layered with
metal electrodes and SWCNT-FE are shown in FIG. 4. The LAP actuator
layered with the SWCNT-FE showed a higher_electric field-induced
strain than an EAP layered with metal electrodes under identical
measurement conditions since the flexible, highly compliant
SWCNT-FE relieves the restraint of the displacement of the
polymeric active layer compared to the metal electrode. In
addition, as explained above, when prepared thin enough, the
SWCNT-FE can be transparent in the visible light range (see FIG.
1B). Actuators fabricated with the transparent SWCNT-FE can be used
in optical devices such as optical switches and modulators.
[0025] As shown in FIG. 4, the out-of-plane strain (S.sub.33)
through the film thickness was plotted as a function of applied
electric field strength. The strain (S.sub.33) of LAP layered with
silver electrodes increased quadratically with increasing applied
electric field, indicating that the strain is mainly
electrostrictively originated. The electrostrictive coefficient
(M.sub.33) vs. LAP layered with silver electrodes, calculated from
a slope in a plot of strain (S.sub.33) vs. the square of electric
field strength (E), S.sub.33=M.sub.33 E.sup.2, was 1.58E-15
m.sup.2/V.sup.2. The strain of EAP layered with SWCNT-FE after
pressing at 600 psi increased more rapidly than that layered with
silver electrodes. The electrostrictive coefficient (M.sub.33) of
this SWCNT-FE system (600 psi) was 3.86E-15 m.sup.2/V.sup.2, more
than 2 times higher than those of EAP layered with silver
electrodes. This significant increase in strain indicates that less
dense SWCNT-FE seemed to restrain the displacement of the active
layer less. Additionally, as the pressure of the fabrication of the
EAP/SWCNT-FE system increased, the strain decreased, since the
SWNT-FE became denser and could constrain the displacement of the
active layer more (FIG. 2A-2C). At 6000 psi, the strain value was
close to that of LAP with the silver electrodes, which indicates
that the modulus of the SWCNT-FE prepared at 6000 psi was close to
that of silver electrodes at the interface.
[0026] Additionally, all-organic electroactive device systems
fabricated with single wall carbon nanotube (SWCNT) films used as
electrodes have shown enhanced electroactive performance in
comparison with conventional electroactive device system fabricated
with metal electrodes. SWCNT can be replaced by multi wall carbon
nanotubes (MWCNT) or few wall carbon nanotubes (FWCNT). Further,
SWCNT film electrodes (SWCNT-FE) have shown reliable capability as
an electrode in an electrical device at high temperatures suitable
for aerospace applications. Additionally, other types of conductive
nanotubes may also be used in these applications, such as boron
nanotubes, boron carbon nitride nanotubes, and/or boron-nitride
nanotubes.
[0027] As explained above, certain mechanical properties of
SWCNT-FE (e.g. Young's modulus) can be controlled by adjusting the
magnitude of the fabrication pressure, to form resultant electrodes
with mechanical properties substantially matching with those of
employed active layers. Additionally, in accordance with at least
one embodiment of the invention, higher mechanical properties (e.g.
Young's modulus, strength, elongation at break, durability,
robustness, etc.) of SWCNT-FE can be achieved by using acid-treated
SWNTs (which are commercially available) and post-sintering at
above 350.degree. C. temperature. A freestanding flexible SWCNT-FE
with high conductivity has been developed. One such inventive
freestanding flexible SWCNT-FE 52 is shown in FIGS. 5A and 5B,
after delamination by breaking the brittle membrane 53. FIG. 5B
shows the freestanding flexible SWCNT-FE 52 sitting on the broken
membrane 53. As explained above, a freestanding SWCNT-FE can be
pressed during the fabrication of a device, or, in the alternative,
it could be independently pressed in order to achieve a desired
thickness, conductivity, compliance, transparency, etc
[0028] As explained above, the thickness of the SWCNT film is
easily controlled by the concentration and quantity of SWCNT
solution, and it can range from about several tens of nanometers to
about several hundreds of micrometers. The SWCNT film which was
thinner than several hundreds of nanometer was found to be
transparent. Therefore, the freestanding flexible transparent SWCNT
film electrodes (SWCNT-FE) enables the inventive all-organic
electroactive devices to be used in optical devices such as optical
switches and modulators.
[0029] Potential applications for an all-organic electroactive
device fabricated with carbon nanotubes, e.g., single wall carbon
nanotube (SWCNT) film electrodes (SWCNT-FE), include
electromechanical energy conversion devices such as
electromechanical sensors and actuators, transducers, sonars,
medical devices, prosthetics, artificial muscles, and materials for
vibration and noise control. The high performance inventive
all-organic electroactive devices possess many advantages over
piezoceramic and shape-memory alloys owing to their light weight,
conformability, high toughness, and tailorable properties needed in
these applications. In addition, the transparency of the novel
all-organic electroactive devices fabricated with SWNT-FE enables
them to be used in optical devices such as optical switches and
modulators. The freestanding flexible SWCNT-FE can provide a great
degree of freedom to fabricate a variety of complex electroactive
devices.
[0030] Although only a few exemplary embodiments of this invention
have been described in detail above, those skilled in the art will
readily appreciate that many modifications are possible in the
exemplary embodiments without materially departing from the novel
teachings and advantages of this invention. Accordingly, all such
modifications are intended to be included within the scope of this
invention as defined in the following claims. Additionally, it
should be understood that the use of the term "invention" herein
should not be limited to the singular, but rather, where
applicable, it is meant to include the plural "inventions" as well.
Further, in the claims, means-plus-function and step-plus-function
clauses are intended to cover the structures or acts described
herein as performing the recited function and not only structural
equivalents, but also equivalent structures.
* * * * *