Polymer actuators using ion-gel electrolytes prepared by self-assembly of ABA-triblock copolymers

Article abstract of DOI:10.1021/ma2022138

Well-defined ABA-triblock copolymers, polystyrene-block-poly(methyl methacrylate)-block-polystyrene (SMS), which have two different polystyrene (PSt) weight fractions (f_PSt), were synthesized by successive atom-transfer radical polymerizations. Ion gels consisting of SMS and an ionic liquid, (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide [C ₂mim][NTf₂]), were prepared using the cosolvent evaporation method with tetrahydrofuran. Atomic force microscope images of the ion gels indicated that PSt is phase-separated to form sphere domains that serve as physical cross-linking points because PSt is not compatible with [C ₂mim][NTf₂], while a continuous poly(methyl methacrylate) (PMMA) phase with dissolved [C₂mim][NTf₂] is formed to serve as ion conduction paths. Accordingly, the ion gels are formed by the self-assembly of SMS and the preferential dissolution of [C₂mim] [NTf₂] into the PMMA phase. The viscoelastic properties of the gels can be easily controlled by changing f_PSt in SMS and [C ₂mim][NTf₂] concentration in the ion gels. The ion gels that exhibit high ionic conductivities (>10^-3 S cm^-1) at room temperature were used as an electrolyte of an ionic polymer actuator, which has a trilaminar structure consisting of the ion-gel electrolyte sandwiched between two composite carbon electrodes containing high-surface-area activated carbon powders. By applying low voltages (<3.0 V) to the electrodes, the actuator exhibited a soft bending motion toward the anodic side.

Full text of DOI:10.1021/ma2022138

Article
pubs.acs.org/Macromolecules
Polymer Actuators Using Ion-Gel Electrolytes Prepared by Self-
Assembly of ABA-Triblock Copolymers
Satoru Imaizumi, Hisashi Kokubo, and Masayoshi Watanabe*
Department of Chemistry and Biotechnology, Yokohama National University, Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan
S
* Supporting Information
ABSTRACT: Well-defined ABA-triblock copolymers, polystyrene-
block-poly(methyl methacrylate)-block-polystyrene (SMS), which
have two different polystyrene (PSt) weight fractions (f PSt), were
synthesized by successive atom-transfer radical polymerizations. Ion
gels consisting of SMS and an ionic liquid, (1-ethyl-3-methylimida-
zolium bis(trifluoromethanesulfonyl)amide [C2mim][NTf2]), were
prepared using the cosolvent evaporation method with tetrahy-
drofuran. Atomic force microscope images of the ion gels indicated
that PSt is phase-separated to form sphere domains that serve as
physical cross-linking points because PSt is not compatible with
[C2mim][NTf2], while a continuous poly(methyl methacrylate)
(PMMA) phase with dissolved [C2mim][NTf2] is formed to serve as
ion conduction paths. Accordingly, the ion gels are formed by the
self-assembly of SMS and the preferential dissolution of [C2mim]-
[NTf2] into the PMMA phase. The viscoelastic properties of the gels can be easily controlled by changing f PSt in SMS and
[C2mim][NTf2] concentration in the ion gels. The ion gels that exhibit high ionic conductivities (>10−3 S cm−1) at room
temperature were used as an electrolyte of an ionic polymer actuator, which has a trilaminar structure consisting of the ion-gel
electrolyte sandwiched between two composite carbon electrodes containing high-surface-area activated carbon powders. By
applying low voltages (<3.0 V) to the electrodes, the actuator exhibited a soft bending motion toward the anodic side.
polymerized in ILs by free-radical polymerization.8 In certain
cases, good compatibility of the resulting polymers with the ILs
1. INTRODUCTION
Ionic liquids (ILs) exhibit unique properties such as thermal
can be achieved, regardless of the polymer concentration and
and (electro)chemical stability, nonvolatility, nonflammability,
temperature. Network polymers containing ILs (ion gels) can
and high ionic conductivity; consequently, they have been an
be obtained in such cases.8 During the same time as our above
research, many other studies investigated the solidification or
gelation of ILs to obtain solid electrolytes by utilizing crystalline
fluorinated copolymers,9 stereocomplex formations of poly-
(methyl methacrylate)s,10 and self-organization of amphiphilic
block copolymers,11 as well as the addition of colloidal
nanoparticles12−14 and low molecular weight gelators.15,16
Among them, the utilization of block copolymers is of great
interest since this methodology may have the potential to afford
easily processable and mechanically strong ion gels by utilizing
self-assembly of the block copolymers. Lodge et al. have been
conducting systematic studies of the preparation, structure,
rheology, and application of ions gels consisting of block
copolymers and ILs.11,17
area of intense interest.1 ILs have received much attention since
Wilkes et al. reported air- and water-stable ILs containing the
tetrafluoroborate anion in 1992.2 ILs are generally regarded as
environmentally benign green solvents and a promising class of
functional materials. The properties of ILs can be adjusted
widely because an infinite number of possible combinations of
cations and anions can be achieved. For this reason, ILs are
sometimes referred to as “designer solvents” and “third
solvents” following water and organic solvents.
From the standpoint of materials science, the combination of
ILs and polymers is promising for the development of novel
materials because certain polymers are compatible with ILs.3−5
The development of polymer electrolytes with unique proper-
ties such as thin-film formability, flexibility, and transparency in
addition to high ionic conductivity has been an intensive topic
of many researchers attempting to realize novel electrochemical
devices.6 In 1993, we published the first report on a polymer
electrolyte containing an IL with an exceptionally high ionic
conductivity.7 This electrolyte was molecular composites
consisting of a chloroaluminate IL and a polymer. Sub-
sequently, we found that common vinyl monomers are widely
soluble in air- and water-stable ILs and that they can be
Applicable fields of ion gels are diverse, e.g., solid electrolytes
of electrochemical devices such as capacitors,18 batteries,19 fuel
cells,20 solar cells,21 and actuators;22−24 membranes for gas
separation25 and catalytic reactions;26 and dielectric layers of
Received: October 3, 2011
Revised: November 25, 2011
Published: December 15, 2011
© 2011 American Chemical Society
401
dx.doi.org/10.1021/ma2022138 | Macromolecules 2012, 45, 401−409

Macromolecules
Article
Scheme 1. Synthesis of SMSs by Successive ATRPs
organic transistors.27 We have been especially interested in
polymer actuators as an application of ion gels. As a material for
manufacturing artificial muscles with biomimetic soft motion,
polymer actuators using electroactive polymer (EAP) have
been applied to manipulators and robotic devices.28−32 Ionic
EAP actuators30−32 driven by diffusion or migration of ions can
exhibit relatively large deformation in response to application of
low voltages. However, these actuators have a serious problem
with regard to their durability under atmospheric conditions
owing to evaporation of solvents, which are necessary to
provide environments that permit the movement of ions. To
overcome such problems, ILs have been applied to the
electrolytes of ionic EAPs.22−24 Most research in this field
has focused on optimization of the electrolytes by changing the
IL structures,33 but very few studies have focused on matrix
polymers for ILs. Indeed, poly(vinylidene fluoride-co-hexa-
fluoropropylene) (P(VDF-co-HFP))24,33a−d and Nafion23,33e
have been mainly investigated in this context. Thus, additional
knowledge regarding the effects of the polymer structure and
properties on the performance of actuators is needed.
In this study, we investigated the microstructures, rheological
properties, and ionic conductivity of ion gels formed by self-
assembly of polystyrene-block-poly(methyl methacrylate)-block-
polystyrene (SMS) triblock copolymers,11c prepared by
successive atom-transfer radical polymerizations (ATRP).34,35
Our previous study showed that polystyrene (PSt) and
poly(methyl methacrylate) (PMMA) were insoluble and
soluble, respectively, in 1-ethyl-3-methylimidazolium bis-
(trifluoromethanesulfonyl)amide ([C2mim][NTf2]);36 thus,
preferential dissolution of [C2mim][NTf2] in the PMMA
phase was expected, which was also confirmed by the study by
Frisbie and Lodge et al.11c The continuous PMMA phase with
dissolved [C2mim][NTf2] may serve as conduction paths for
the IL, while the phase-separated PSt phase may serve as
physical cross-linking points. Furthermore, we report the
performance of the polymer actuators using ion-gel electrolytes
consisting of SMS and [C2mim][NTf2]. Chemically deposited
noble-metal electrodes23,30 and carbon nanotubes,24,37 have
been widely used as electrode materials for ionic EAPs. We
have proposed that inexpensive and ubiquitous carbon
materials such as activated carbon can be used as electrode
material of the actuators.38 Here, we demonstrate an ionic EAP
actuator with a trilamellar structure consisting of an ion-gel
electrolyte sandwiched between two composite carbon electro-
des containing high-surface-area activated carbon powders. The
correlation between the actuator performance and the proper-
ties of the ion gels is also discussed.
2. EXPERIMENTAL SECTION
Materials. An ionic liquid, [C2mim][NTf2], was prepared
according to the literature with slight modification39 and dried
under vacuum at 100 °C for 24 h. The water content in
[C2mim][NTf2] determined by Karl Fischer titration was less than
10 ppm. 2-Bromoisobutyl bromide, dehydrated anisole, and 4,4′-
dinonyl-2,2′-bipyridine (dNbpy) were purchased from Aldrich and
used without further purification. CuBr and CuBr2 were purchased
from Wako Chemical. CuBr was washed with glacial acetic acid,
dehydrated ethanol, and diethyl ether, dried under vacuum, and then
stored in an argon-atmosphere glovebox (VAC). CuBr2 was dried
under vacuum and stored in the same drybox. Ethylene glycol,
triethylamine and N,N,N′,N′,N″-pentamethyldiethylenetriamine
(PMDETA) were purchased from Tokyo Chemical Industry, and
were dried by molecular sieves. Methyl methacrylate (MMA) and
styrene (both from Wako Chemical) were dried by calcium hydride
overnight and vacuum-distilled prior to use.
Synthesis of a Bifunctional Initiator. A bifunctional initiator,
ethylene glycol bis(2-bromoisobutyrate), was synthesized according to
the literature.40 To accomplish this, ethylene glycol (5.6 mL, 0.10 mol)
and triethylamine (34 mL, 0.24 mol) were dissolved in 300 mL of
diethyl ether in a three-necked flask under a N2 atmosphere, after
which the solution was cooled to 0 °C in an ice bath. Next, 2-
bromoisobutyl bromide (30 mL, 0.24 mol) was dropped into the
solution, and the solution was stirred overnight. The reaction solution
was then filtered, after which the filtrate was washed with water three
times. Finally, white needle crystals (14 g, 39 mmol, yield 39%) were
obtained by recrystallization from ethanol/H2O. 1H NMR of the
bifunctional initiator (400 MHz, CDCl3): δ (ppm) = 1.94 (s,
(CH3)2C, 12H), 4.44 (s, OCH2, 4H). (The spectrum is shown in
Supporting Information, Figure S-1)
Synthesis of PMMA Macroinitiator. The bifunctional initiator
(1.7 g, 4.8 mmol) and CuBr2 (2.5 mg, 0.24 mmol) were dried under
reduced pressure in a three-necked flask. Anisole (200 mL) and
PMDETA (0.63 μL, 3.0 mmol) were then added to the flask. To
dissolve CuBr2 by complex formation with PMDETA, the solution was
stirred overnight at 60 °C under a N2 atmosphere. After cooling the
solution, CuBr (0.34 mg, 2.4 mmol) and MMA (200 mL, 1.9 mol)
were added to the flask. The reaction mixture was then degassed by
sonication under reduced pressure and successive N2 replacement
three times. A polymerization reaction was subsequently conducted at
60 °C for 6 h with stirring (Scheme 1). Next, the reaction was
quenched by cooling to 0 °C, after which the crude polymer was
isolated by precipitation into an excess amount of methanol and
collected by suction filtration. The polymer was then dissolved again in
ethyl acetate and the solution was purified by column chromatography
(alumina) to remove the Cu complexes from the PMMA. The eluted
ethyl acetate solution of the PMMA was poured into a large excess of
hexane, and the precipitates were filtered and dried under vacuum.
The purified PMMA macroinitiator was obtained as white powder
(Yield: 90 g). The molecular characterization results are shown in
Table 1.
402
dx.doi.org/10.1021/ma2022138 | Macromolecules 2012, 45, 401−409

Macromolecules
Article
sliced into a thin film to expose the cleaved face for the AFM
observation. The ionic conductivity of the ion gels was determined
from complex impedance measurements using a Hewlett-Packard
4192A LF impedance analyzer over a frequency range of 5 Hz to 13
MHz. The ion gel samples were then placed between two stainless
steel disk electrodes separated by a polytetrafluoroethylene spacer with
an inner diameter of 8.5 mm and a height of 3 mm. The cell constant
was determined using a 0.01 M KCl standard aqueous solution. The
sample cell was placed in a thermo-regulated bath and thermally
equilibrated at each temperature for at least 1 h before taking the
measurements.
Preparation and Measurement of Ion Gel Actuators.
Preweighed amounts of SMS and [C2mim][NTf2] were dissolved in
tetrahydrofuran (THF) as a cosolvent. After casting the THF solution
in a flat Petri dish, the THF was gradually removed from the solution
at ambient temperatures and then dried under vacuum for more than
12 h. Transparent and flexible ion gel membranes (SMS/[C2mim]-
[NTf2] composites) were obtained by this procedure.
Ion gel actuators have a trilaminar structure consisting of an ion-gel
electrolyte membrane sandwiched between two carbon electrodes.
The carbon electrodes were prepared by mixing activated carbon (24
wt %, Kuraray Co. Ltd.), Ketjen black (3 wt %, Lion Corp.), P(VDF-
co-HFP) (8 wt %, Arkema Inc.), and [C2mim][NTf2](65 wt %) using
a conditioning mixer (AR-250, Thinky). The mixture was then hot
pressed with a polyimide spacer (50 μm) at 130 °C. Next, ion gel
membranes with a thickness of 100 μm were fabricated by hot pressing
at 130−160 °C, and the electrode membranes were attached to both
sides of the ion-gel electrolyte by hot pressing at 80−130 °C to
fabricate a monolithic trilaminar membrane. The thickness of the
actuators became a little thinner (ca. 10 μm) than the total thickness of
the electrodes and the electrolyte by the final hot pressing. Rectangular
pieces (width of 2 mm and length of 7 mm) were cut from the
monolithic membrane and clipped between Cu tapes connected to a
potentiostat (HA-301, Hokuto Denko) and a function generator (HB-
104, Hokuto Denko). Displacement of the actuator was measured at
room temperature by a laser displacement meter (LC-2440, Keyence)
at 4 mm from the clamped end.
Table 1. Monomer Conversion, Molecular Weight,
Molecular Weight Distribution, and Composition of PMMA
and SMSs
Mn,theo
Mn
f PSt
d
a
b
c
convn
( × 10−4)
( × 10−4) Mw/Mn
(wt %)
e
f
c
PMMA
0.47
1.9
2
1.89
2.31
3.65
1.12
1.11
1.16
−
18.3
g
f
f
f
SMS-18
SMS-48
0.1
g
f
0.3
4
48.2
a
b
Monomer conversion. Calculated from monomer conversion.
c
d
Evaluated by GPC analysis using PMMA standard. Weight fraction
e
f
of PSt in the SMS. Utilized as a macroinitiator for SMSs. Calculated
by H NMR analysis. Calculated from polymer yield.
g
1
Synthesis of ABA-Triblock Copolymers. The synthesized
PMMA macroinitiator (20 g, 1.1 mmol), CuBr (0.13 g, 0.87 mmol),
CuBr2 (5.8 mg, 0.026 mmol), and dNbpy (0.76 g, 1.9 mmol) were
added into a dried round-bottom flask. Styrene (80 mL, 0.69 mol),
which is not only a monomer but also a reaction solvent, was then
poured into the flask. The polymerization reaction was then allowed to
proceed at 100 °C. At 26 and 45 h from the initiation of the
polymerization, heating was stopped. The obtained polymer was then
isolated and purified by reprecipitation using a similar method as that
used for the PMMA macroinitiator. The weight fractions of PSt in
1
SMS-18 and SMS-48 were evaluated from H NMR spectra shown in
Figure S-2, Supporting Information. The molecular characterization
results of the block copolymers are shown in Table 1. Gel permeation
chromatograms (GPC) of the PMMA macroinitiator and ABA-triblock
copolymers (Figure 1) indicated that well-defined block copolymers
were prepared by the successive ATRP method.
3. RESULTS AND DISCUSSION
Formation of Ion Gels. It is interesting to explore how
effectively [C2mim][NTf2] gelates with the addition of SMS
block copolymers. The gelation point of the SMS and
[C2mim][NTf2] binary systems was evaluated by dynamic
viscoelastic measurement. The dynamic rheological properties
measured under a constant strain amplitude within a linear
viscoelastic regime are shown in Figure 2. The 7 wt %
dispersions are liquids for both SMS block copolymer systems;
the viscous modulus (G″) exceeds the elastic modulus (G′) over
the entire frequency range, and both moduli exhibit depend-
ence on frequency. The dispersions show a complicated
response at 9 wt % for SMS-18 and at 8 wt % for SMS-48.
Specifically, the moduli exhibit a crossover at a high frequency.
However, G′ is dominant and the moduli become relatively
independent of frequency toward the low end of the frequency
spectrum. At 9 wt % for SMS-48, G′ is larger than G″ and
becomes less dependent on frequency over the entire measured
range. These findings indicate that dispersions containing
greater than 9 wt % for SMS-18 and more than 8 wt % for
SMS-48 behave as soft solid materials (ion gels). In appearance,
binary systems containing SMS at levels just below the gelation
concentrations were bluish viscous liquids because of Rayleigh
scattering, and these systems became extremely viscous as they
approached gelation. Binary systems containing SMS at levels
higher than the gelation concentrations became transparent and
colorless gels.
Figure 1. Gel permeation chromatograms of PMMA macroinitiator
and SMS block copolymers.
Material Characterization. Viscoelastic measurements were
conducted using a Physica MCR301 (Anton Paar) rotary rheometer
with an H-PTD200 temperature controller. A parallel plate (25 or 50
mm diameter) was installed, depending on the modulus of each
sample. The frequency dispersion was measured in the frequency
range of 0.1 to 100 rad s−1 and in the temperature range from 120 to 0
°C by 10 °C steps. The samples were thermally equilibrated at each
temperature for at least 1 h before the measurements. Differential
scanning calorimetry (DSC) was conducted using a Seiko Instruments
DSC 6220 under a nitrogen atmosphere. The samples were tightly
sealed in aluminum pans in the dry glovebox. The DSC measurements
were conducted by heating to +150 °C, cooling to −150 °C, and then
heating to +150 °C at a cooling and heating rate of 10 °C min−1. The
glass transition temperatures (Tg) were determined from the mid
points of heat capacity changes in the DSC thermograms during the
programmed reheating scans. Atomic force microscope (AFM) images
were recorded at room temperature by an SPA-400 microscope unit
and a SPI3800N probe controller (Seiko Instruments Inc.) in tapping
mode, using a silicon cantilever with a spring constant of 15 N m−1. A
lump of the ion gel sample was frozen with liquid N2, cleaved, and
403
dx.doi.org/10.1021/ma2022138 | Macromolecules 2012, 45, 401−409

Macromolecules
Article
Figure 3. Temperature dependence of G′ and G″ of ion gels based on
SMS-48 (10 wt %) and SMS-18 (10 wt %) at 1 rad/s.
appears the sol−gel transition temperature. Conversely, the
SMS-48 ion gel displays no transition over the measured
temperature (0−120 °C). This phenomenon indicates that the
PSt domain remains aggregated even above its Tg (=ca. 90 °C)
with molecular weight of 9 kDa,41 because PSt is less
compatible with [C2mim][NTf2]. The difference in the sol−
gel transition behavior of SMS-18 and SMS-48 appears to be
caused by the difference in the incompatibility between PSt and
[C2mim][NTf2], which strongly depends on the molecular
weight of PSt blocks. Strain dependencies of the viscoelastic
moduli are shown in Figure 4. A linear regime was maintained
Figure 2. Storage (G′) and loss (G″) moduli as a function of frequency
for binary systems consisting of [C2mim][NTf2] and SMS-18 (a) or
SMS-48 (b) at 20 °C.
Lodge et al. reported that gelation of an IL, 1-butyl-3-
methylimidazolium hexafluorophosphate ([C4mim]PF6), could
be achieved by the self-assembly of as little as 5 wt % of a
triblock copolymer, PSt-block-poly(ethylene oxide)(PEO)-
block-PSt (SOS), where Mn of the each terminal PSt is 4760
Da, Mn of the middle PEO is 25 500 Da, the polydispersity
index (Mw/Mn) is 1.36, and the PSt weight fraction (fPSt) is
0.28.11a Although there are differences in the IL-philic segment
structure; PEO against PMMA, and in the IL structures;
[C4mim]PF6 against [C2mim][NTf2], the critical gelation
concentrations of these block copolymers are comparable.
The somewhat lower gelation concentration of SOS than that
of SMS may be ascribed to its higher Mn of the IL-philic PEO
segment. They also recently reported physical properties of
[C2mim][NTf2] ion-gels with the 10 wt % addition of an SMS
block copolymer (Mn of the SMS = 121 kDa, f PSt = 0.29).11c
Figure 3 shows the viscoelastic moduli (G′ and G″) of the ion
gels containing 10 wt % SMSs as a function of temperature in
the range of 0 to 120 °C at a frequency of 1 rad/s. The SMS-18
ion gel exhibits a crossing of G′ and G″ at around 50 °C, where
the sol−gel transition occurs. This sol−gel transition temper-
ature is almost the same as Tg of PSt (= ca. 50 °C) with
molecular weight of 2 kDa,41 however, it depends on the
angular frequency, as shown in Figure S-3, Supporting
Information. SMS concentrations also affect the sol−gel
transition temperatures (Figure S-4, Supporting Information).
These results indicate that the stability of PSt cross-linking
points cannot be explained only by the magnitude of Tg. The
higher is the concentration or angular frequency, the higher
Figure 4. G′ and G″ as a function of strain for ion gels containing 15 wt
% of SMS-18 or SMS-48 at 25 °C and 1 Hz.
for up to 10% strain for each ion gel. By applying larger strain,
the polymer networks were broken, possibly because of
slipping-off of PSt chains from PSt domains that serve as
physical cross-linking points of the ion gels. The plateau G′ of
the SMS-18 composite and SMS-48 composite are 7 and 9 kPa,
respectively. The higher tan δ (=G″/G′) value of the SMS-18
composite than that of the SMS-48 composite suggests that the
number of looped chains, which are dominant in the sol state
and ineffective in the formation of the gels, remains in a larger
quantity in the SMS-18 composite. This is supported by the
fact that deviation from the G′ values of ideal gels is larger for
SMS-18 than that for SMS-48 (Figure S-5, Supporting
Information). The ion gel formed by SMS-48 has a higher
cross-linking density than that formed by SMS-18, resulting in a
hard and brittle gel.
404
dx.doi.org/10.1021/ma2022138 | Macromolecules 2012, 45, 401−409

Macromolecules
Article
Microstructure and Ionic Conductivity of Ion Gels. To
confirm selective dissolution of [C2mim][NTf2] in PMMA
segments, which was expected from the observations in the
rheological measurements (vide supra), we conducted DSC
measurements of the ion gels. The DSC thermograms for SMS-
48/[C2mim][NTf2] are shown in Figure S-6, Supporting
Information. The Tg values and the transition widths
determined from the onsets and ends of heat capacity changes
are listed in Table S-1, Supporting Information. Figure 5 shows
Figure 6. Tapping-mode AFM phase image of an ion gel based on
SMS-48 (30 wt %).
ring-shaped 2D Fourier power spectrum is obtained, which
indicates that the microphase separated structure of the ion gel
does not have a fully ordered cubic structure, but rather a short-
range ordered structure. Since phase diagram of block
copolymers is well understood,43 it is interesting to know the
factors that determine the phase behavior and ordered/
disordered structures. In the case of ordinary block copolymers,
the ordered/disordered structures depend on the compatibility
and segment size of each block.43 Strongly segregated systems
with less compatible blocks with large segment size take
ordered structures. In the present case, quantitative compati-
bility of [C2mim][NTf2] with PMMA and further that between
PSt and PMMA with dissolved [C2mim][NTf2] remains
unexplored at a fundamental level.5b We just speculate now
that the segregation between PSt and PMMA with dissolved
[C2mim][NTf2] is not strong enough to form a fully ordered
structure.
Figure 5. Tg of ion gels based on SMS-48 as a function of weight
fraction of [C2mim][NTf2].
the Tg values of ion gels based on SMS-48 plotted against
[C2mim][NTf2] weight fractions. In the case of neat SMS-48,
only one Tg is observed at ca. 100 °C. We can not distinguish
Tg values of PSt and PMMA because they are close together. As
the weight fraction of [C2mim][NTf2] increases, one Tg is still
retained at ca. 100 °C, whereas another Tg appears at lower
temperatures. In [C2mim][NTf2] composition range of 30−50
wt %, the heat capacity changes corresponding to the lower Tgs
are broadened (Figure S-6 and Table S-1, Supporting
Information). Lodge et al. recently reported that PMMA/
[C2mim][NTf2] solutions have two apparent glass transitions
at intermediate compositions, even if the binary systems are
good solvent solutions.42 We also observed similar phenomena
in the network PMMA with dissolved [C2mim][NTf2].8b,c In
the present case, the broadening may also be caused by the
coexistence of PMMA-rich region and [C2mim][NTf2]-rich
region. When the weight fraction of [C2mim][NTf2] becomes
higher than 0.8, Tg at ca. 100 °C disappears and only one Tg
appears at low temperature. When the weight fraction of
[C2mim][NTf2] becomes high, Tg of PSt cannot be observed
because of a small heat capacity change accompanied by glass
transition of PSt.
Figure 7 shows the Arrhenius plot of ionic conductivities for
the ion gels. The conductivity values were calculated from a cell
Figure 6 shows a tapping-mode AFM phase image of an ion
gel containing 30 wt % of SMS-48. In this image, the bright
region indicates a softer and more attractive surface, while the
dark region indicates a harder and less-attractive surface. As
expected, the image clearly shows that the ion gel is phase-
separated between soft and hard domains.43 The continuous
bright portions and spherical dark portions correspond to
PMMA(15 wt %) with dissolved [C2mim][NTf2](70 wt %)
domains and PSt(15 wt %) domains, respectively. In this case,
the PSt spheres did not appear to form a fully ordered structure
from the AFM image. Figure S-7 (Supporting Information)
shows a two-dimensional (2D) Fourier power spectrum
corresponding to the AFM image (Figure 6). An obscurely
Figure 7. Arrhenius plots of ionic conductivity for the ion gels based
on the SMS block copolymers with dissolved [C2mim][NTf2].
constant and the real part of cell impedance value (Z′) where
the imaginary part of cell impedance (−Z″) takes a minimum in
the Nyquist plots (Z′ vs −Z″ plots). Typical Nyquist plots are
405
dx.doi.org/10.1021/ma2022138 | Macromolecules 2012, 45, 401−409

Macromolecules
Article
as shown in Figure S-8, Supporting Information, which consist
of a low frequency spur corresponding to the interfacial
impedance and a high frequency arc corresponding to the bulk
impedance. There were no significant changes in the shape of
the Nyquist plots with temperature, polymer concentration,
and f PS of SMS. Room temperature ionic conductivities of the
gels reach 10−3 S cm−1, and the temperature dependencies can
be represented by the Vogel−Fulcher−Tammann (VFT)
equation. On the basis of the VFT equation and the best-fit
parameters (Supporting Information, Table S-2), the lines on
the plots reproduce the experimental data well. It is also
interesting to note that the ion gel based on SMS-18 exhibits
continuous conductivities expressed by the VFT equation from
−10 to +100 °C, even though the binary system undergoes a
sol−gel transition at ca. 50 °C, as shown in Figure 3. This is
contrasted by the previous observation that gel electrolytes
based on ABA block copolymers, polyethylene-block-poly-
(ethylene oxide-co-propylene oxide)-block-polyethylene, and a
1 M Li[NTf2] solution in γ-butyrolactone.44 The gel electro-
lytes exhibit discontinuous conductivity changes at the sol−gel
transition temperatures owing to melting of the end-poly-
ethylene-blocks. In this case, there should be certain
interactions between the Li salts and the midpolyether-blocks,
which result in discontinuous conductivity increases at gel-to-
sol transitions owing to melting of the end-blocks. Conversely,
the [C2mim][NTf2] consists of extremely weak Lewis acidic
cations and Lewis basic anions.45 Thus, the motion of
[C2mim][NTf2] is relatively decoupled from the motion of
PMMA segments,8c and the melting of end-PSt-blocks does not
contribute to acceleration of the transport of [C2mim][NTf2].
The ionic conductivities of the SMS-48 ion gels are higher
than those of SMS-18 ion gels at the same block copolymer
compositions. Since we have reported the ionic conductivities
of loosely cross-linked PMMA networks with dissolved
[C2mim][NTf2],8b we simulated the ionic conductivities of
SMS ion gels based on a two-phase model composed of
continuous PMMA domains with dissolved [C2mim][NTf2]
and isolated PSt domains. This two-phase model assumes
complete phase separation between these two phases. The
conductivity can be written as
Figure 8. Ionic conductivity at 20 °C as a function of weight fraction
of SMS for the ion gels containing [C2mim][NTf2]. Broken line:
σ(PMMA + [C2mim][NTf2]) from ref8b; Solid line: ϕ σ(PMMA
+[C2mim][NTf2]). Solid plots: experimental data.
interaction with PMMA chains,8b the ionic mobility is mainly
determined by the PMMA/[C2mim][NTf2] compositions.
Performance of Polymer Actuator Using Ion Gels. The
self-assembly of the SMS block copolymers in an IL was shown
to form highly ion-conductive and nonvolatile soft-materials
(ion gels). Here, we show an application of the ion gels to ionic
EAP actuators. Figure 9 shows the current and bending
σ = ϕσ(PMMA + [C2mim][NTf2]) + (1 − ϕ)σ(PSt)
where ϕ is the volume fraction of the PMMA domains with
dissolved [C2mim][NTf2]. Because of the negligibly low
conductivity of σ(PSt), the above equation can be rewritten as
σ = ϕσ(PMMA + [C mim][NTf ])
2
2
The broken lines in Figure 8 show σ(PMMA + [C2mim]-
[NTf2]) determined from our data,8b and the solid lines
represent ϕ σ(PMMA + [C2mim][NTf2]). Both of these values
are plotted against the weight fraction of SMS in the ion gels.
As shown in the figure, the ϕ (volume fraction of the PMMA/
[C2mim][NTf2]) has little effect on the σ values. The
experimental data shown by solid plots are reasonably located
along the solid lines, and interference of the ion transport by
the PSt domains appears to be very small. The higher
conductivity for the SMS-48 ion gels than the SMS-18 ion
gels shown in Figure 7 simply comes from the fact that the
PMMA phase in the SMS-48 ion gel contains larger amounts of
[C2mim][NTf2] at the same SMS weight fraction and thus
exhibits higher σ(PMMA + [C2mim][NTf2]). This effect
overwhelms the small ϕ for the SMS-48 ion gels. Since the
ionic diffusion of [C2mim][NTf2] is interrupted by the
Figure 9. Current and displacement responses of an ion gel actuator
based on SMS-18 (20 wt %) against application of 2.0 V rectangular
voltage with a cycle of 100 s.
displacement responses of an ion gel actuator against a
rectangular voltage application (see also Figure S-9, Supporting
Information). When voltage is applied to the actuator, charging
current is observed, but this current decays exponentially with
time. No faradaic current was observed in the cyclic
406
dx.doi.org/10.1021/ma2022138 | Macromolecules 2012, 45, 401−409

Macromolecules
Article
voltammetry within the voltage range of 2.0 V. These
phenomena indicate that charging and discharging of the
electric double layer formed at the interface between the
activated carbon and [C2mim][NTf2] in the electrode layer is
responsible for displacement of the actuator. It should be noted
that the bending displacement is always directed toward the
anodic side. In other words, the actuator bends toward the
positively polarized electrode direction. This behavior has been
widely observed in ionic EAP actuators using ILs.23,24,33,46 We
have investigated the transport properties of common ionic
liquids in detail, especially imidazolium-based ILs.47 Interest-
ingly, the diffusivity of the cations is larger than that of anions
in most cases, even if the van der Waals radius of the cations is
larger than that of the anion.47c Typically, the cationic and
anionic diffusivity of [C2mim][NTf2] is clarified to be 4.4 ×
10−7 and 2.5 × 10−7 cm2 s−1, respectively, at 20 °C,47c which
corresponds to a cationic transference number of 0.64. The
cationic transference number in the PMMA-based ion gels also
becomes larger as the mole fraction of [C2mim][NTf2]
decreases (increasing the mole fraction of PMMA) owing to
preferential interaction of the [NTf2] anion with PMMA
chains.8b Such imbalanced transport between the cation and
anion induces concentration polarization of [C2mim][NTf2]
inside the polymers (PMMA in the electrolyte layer and
P(VDF-co-HFP) in the electrode layer) via electrochemical
polarization of the actuators. On the anodic side, the
concentration becomes lower than that in the bulk, while on
the cathodic side, it becomes larger than that in the bulk. This
concentration polarization causes swelling of the cathodic
electrode layer and deswelling of the anodic electrode layer,
which appears to explain such displacement. The actuation
mechanism will be discussed in detail in a forthcoming paper.
The applied voltage dependence of the displacement of the
ion gel actuators is shown in Figure 10. As the applied voltages
V,39,48 the actuator experiments were conducted under
atmospheric conditions and the contamination by water and
oxygen could cause to reduce the electrochemical stability of
the actuator. Figure 11 shows the displacement amplitude of
Figure 11. Scan rate dependence of the displacement amplitude for
ion gel actuators based on SMS block copolymers with the application
of 1.5 V triangular wave voltage.
the actuators with the application of 1.5 V triangular wave
voltage as a function of the scan rate and a function of the
frequency (upper horizontal axis). The actuator based on SMS-
48 demonstrates superior performance in terms of displace-
ment amplitude and speed. These results reflect the difference
in the electrolyte properties. Specifically, the ionic conductiv-
ities of the ion gels containing 20 wt % of SMS-48 and SMS-18
at 20 °C are 2.4 × 10−3 and 1.7 × 10−3 S cm−1, respectively.
Higher conductivity makes the time constants of the actuators
smaller, which enhances the amount of electricity stored at the
electric double layers and the magnitude of concentration
polarization of [C2mim][NTf2] at a constant voltage scan rate.
The simplest equivalent circuit for the actuators is the series
connection of a resistance and a capacitance. The resistance (R)
correlates with the conductivity and shape of ion gels and the
capacitance (C) corresponds to the double layer capacitance
between the ion gel and carbon electrodes. Actual R and C
values of the actuator were estimated to be R = 40 Ω and C =
0.1 F for an ion gel actuator based on SMS-18 (20 wt %), which
is shown in Figure 9. In this case, the time constant becomes 4
s. However, the displacement in Figure 9 continues to increase
for several tens of seconds. In the actuation experiments, one
end of a rectangular trilaminar-specimen was clipped between
Cu current-collectors. The carbon electrode layer is much more
resistive compared with the metal. Consequently, the potential
drop along longitudinal direction of the actuator specimen
cannot be neglected. This is the main reason why the time
constant of the actuator during actuation becomes longer than
that estimated from the R and C values. However, for fast and
large movement of the actuators, reduction of the time constant
by the achievement of high ionic conductivity of the ions gels
and large double-layer capacitance as well as the achievement of
high electronic conductivity of the carbon electrodes appears to
be the most crucial requirements.
Figure 10. Displacement of ion gel actuators based on SMS block
copolymers as a function of the magnitude of rectangular-wave
voltages at a cycle of 100 s.
increase, electric charges stored in the electric double layer
increase, resulting in an increase in displacement up to ca. 1.6
mm at 3.0 V, which is 40% of its length. However, when a
voltage of 3.5 V is applied, the displacement does not change or
decreases slightly, despite an increase in the flowing current.
Reversibility of motion of the actuators also deteriorated at an
applied voltage of 3.5 V. This is due to certain irreversible
faradaic reactions. Although the electrochemical potential
window [C2mim][NTf2] is reported to be wider than 4
CONCLUSION
■
We investigated the gelation of an IL, [C2mim][NTf2], by self-
assembly of SMS block copolymers. The rheological properties,
AFM images, and ionic conductivity of the SMS/[C2mim]-
407
dx.doi.org/10.1021/ma2022138 | Macromolecules 2012, 45, 401−409

Macromolecules
Article
Chem. Soc. 2005, 127, 4976. (c) Seki, S.; Susan, M. A. B. H.; Kaneko,
T.; Tokuda, H.; Noda, A.; Watanabe, M. J. Phys. Chem. B 2005, 109,
3886.
(9) (a) Carlin, R. T.; Fuller, J. Chem. Commun. 1997, 1345.
(b) Fuller, J.; Breda, A. C.; Carlin, R. T. J. Electrochem. Soc. 1997, 144,
L67. (c) Fuller, J.; Breda, A. C.; Carlin, R. T. J. Electroanal. Chem.
1998, 459, 29.
[NTf2] binary systems are reasonable if we assume that the
gelation occurs via aggregation of the PSt segments in the IL
owing to incompatibility with [C2mim][NTf2] and that the
resulting ion gels have two-phase structures consisting of
continuous PMMA phases with preferentially dissolved
[C2mim][NTf2] and isolated PSt phases. The aggregated PSt
phases serve as physical cross-linking points of the ion gels.
Moreover, we fabricated ionic EAP actuators using SMS/
[C2mim][NTf2] ion gels. The ion gel actuators have a
trilaminar structure composed of the ion-gel electrolyte
sandwiched between two composite carbon electrodes
containing high-surface-area activated carbon powders. By
applying low voltages (<3.0 V) to the electrodes, the actuator
exhibited soft bending motion toward the anodic side. The
displacement of the actuator increased with an increase in the
charge stored at the electric double layer between the activated
carbon and the IL, eventually increasing to 40% of its length.
The ionic conductivity of the ion gels was closely correlated
with the performance of the actuators.
(10) Kawauchi, T.; Kumaki, J.; Okoshi, K.; Yashima, E. Macro-
molecules 2005, 38, 9155.
(11) (a) He, Y.; Boswell, P. G.; Buhlmann, P.; Lodge, T. P. J. Phys.
̈
Chem. B 2007, 111, 4645. (b) Lodge, T. P. Science 2008, 321, 50.
(c) Zhang, S.; Lee, K. H.; Frisbie, C. D.; Lodge, T. P. Macromolecules
2011, 44, 940.
(12) (a) Hasegawa, K.; Tatsumisago, M.; Minami, T. J. Electrochem.
Soc. 1999, 146, 3359. (b) Wang, P.; Zakeeruddin, S. M.; Comte, P.;
Exner, I.; Gratzel, M. J. Am. Chem. Soc. 2003, 125, 1166. (c) Usui, H.;
̈
Matusi, H.; Tanabe, N.; Yanagida, S. J. Photochem. Photobiol. A 2004,
164, 97. (d) Katakabe, T.; Kawano, R.; Watanabe, M. Electrochem.
Solid-State Lett. 2007, 10, F23.
(13) (a) Ueno, K.; Inaba, A.; Kondoh, M.; Watanabe, M. Langmuir
2008, 24, 5253. (b) Ueno, K.; Hata, K.; Katakabe, T.; Kondoh, M.;
Watanabe, M. J. Phys. Chem. B 2008, 112, 9013. (c) Ueno, K.;
Imaizumi, S.; Hata, K.; Watanabe, M. Langmuir 2009, 25, 825.
(d) Ueno, K.; Inaba, A.; Sano, Y.; Kondoh, M.; Watanabe, M. Chem.
Commun. 2009, 3603. (e) Ueno, K.; Sano, Y.; Inaba, A.; Kondoh, M.;
Watanabe, M. J. Phys.Chem. B 2010, 114, 13095. (e) Ueno, K.;
Watanabe, M. Langmuir 2011, 27, 9105.
(14) (a) Shimano, S.; Zhou, H.; Honma, I. Chem. Mater. 2007, 19,
5216. (b) Lee, U.-H.; Kudo, T.; Honma, I. Chem. Commun. 2009,
3068.
(15) Hanabusa, K.; Fukui, H.; Suzuki, M.; Shirai, H. Langmuir 2005,
21, 10383.
ASSOCIATED CONTENT
■
S
* Supporting Information
Characterization of materials (Figure S-1 and S-2), rheological
properties (Figure S-3, S-4, and S-5), thermal properties (Table
S-1 and Figure S-6), two-dimensional Fourier power spectrum
of a tapping mode AFM phase image (Figure S-7), ionic
conductivity (Figure S-8 and Table S-2), and photographs of
the movement of an ion gel actuator (Figure S-9). This material
is available free of charge via the Internet at http://pubs.acs.org.
(16) (a) Kimizuka, N.; Nakashima, T. Langmuir 2001, 17, 6759.
(b) Ikeda, A.; Sonoda, K.; Ayabe, M.; Tamaru, S.; Nakashima, T.;
Kimizuka, N.; Shinkai, S. Chem. Lett. 2001, 1154.
AUTHOR INFORMATION
■
Corresponding Author
*Telephone and fax: +81-45-339-3955. E-mail: mwatanab@
ynu.ac.jp.
(17) (a) He, Y.; Lodge, T. P. Chem Cmmun. 2007, 2732. (b) He, Y.;
Lodge, T. P. Macromolecules 2008, 41, 167.
́
(18) (a) Lewandowski, A.; Swiderska, A. Solid State Ionics 2003, 161,
243. (b) Isshiki, Y.; Nakamura, M.; Tabata, S.; Dokko, K.; Watanabe,
M. Polym. Adv. Tech. 2011, 22, 1254.
ACKNOWLEDGMENTS
■
(19) (a) Shobukawa, H.; Tokuda, H.; Susan, M.; Watanabe, M.
Electrochim. Acta 2005, 50, 3872. (b) Shin, J.-H.; Henderson, W. A.;
Passerini, S. J. Electrochem. Soc. 2005, 152, A978. (c) Ye, H.; Huang, J.;
Xu, J. J.; Khalfan, A.; Greenbaum, S. G. J. Electrochem. Soc. 2007, 154,
A1048.
(20) (a) Lee, S.-Y.; Yasuda, T.; Watanabe, M. J. Power Sources 2010,
195, 5909. (b) Lee, S.-Y.; Ogawa, A.; Kanno, M.; Nakamoto, H.;
Yasuda, T.; Watanabe, M. J. Am. Chem. Soc. 2010, 132, 9764.
This work was supported in part by Grants-in-aid for Scientific
Research on Priority Areas (No. 438-19016014 and No. 452-
17073009) from the MEXT of Japan.
REFERENCES
■
(1) (a) Welton, T. Chem. Rev. 1999, 99, 2071. (b) Holbrey, J. D.;
Seddon, K. R. Clean Prod. Process 1999, 1, 223. (c) Wasserscheid, P.;
Keim, W. Angew. Chem., Int. Ed. 2000, 39, 3772. (d) Wilkes, J. S. Green
Chem. 2002, 4, 73. (e) Seddon, K. R. Nat. Mater. 2003, 2, 363.
(f) Plechkova, N. V.; Seddon, K. R. Chem. Soc. Rev. 2008, 37, 123.
(2) Wilkes, J. S.; Zaworotko, M. J. J. Chem. Soc., Chem. Commun.
1992, 965.
(3) Ionic liquids in Polymer Systems: Solvents, Additives, and Novel
Applications; ACS Symposium Series 913; Brazel, C. S., Rogers, R. D.,
Eds.; American Chemical Society: Washington DC, 2005.
(4) Winterton, N. J. Mater. Chem. 2006, 16, 4281.
(5) (a) Ueki, T.; Watanabe, M. Macromolecules 2008, 41, 3739.
(b) Ueki, T.; Watanabe, M. Bull. Chem. Soc. Jpn. 2011, DOI: 10.1246/
bcsj.20110225.
(6) (a) Polymer Electrolyte Reviews 1 and 2; MacCallum, J. R.,
Vincent, C. A., Eds.; Elsevier: London, 1987 and 1989. (b) Gray, F. M.
Solid Polymer Electrolytes; VCH Publishers: New York, 1991. (c)
Application of Electroactive Polymers; Scrosati, B., Ed.; Chapman &
Hall: London, 1993.
(21) (a) Wang, P.; Zakeeruddin, S. M.; Exnar, I.; Gratzel, M. Chem.
Commun. 2002, 2972. (b) Kawano, R.; Katakabe, T.; Shimosawa, H.;
̈
Nazeeruddin, M. K.; Gratzel, M.; Matsui, H.; Kitamura, T.; Tanabe,
̈
N.; Watanabe, M. Phys. Chem. Chem. Phys. 2010, 12, 1916.
(22) (a) Lu, W.; Fadeev, A. G.; Qi, E.; Smela, B. H.; Mattes, B. R.;
Ding, J.; Spinks, G. M.; Mazurkiewicz, J.; Zhou, D. Z.; Wallace, G. G.;
MacFarlane, D. R.; Forsyth, S. A.; Forsyth, M. Science 2002, 297, 983.
(b) Zhou, D.; Spinks, G.; M. Wallace, G. G.; Tiyapiboonchaiya, C.;
MacFarlane, D. R.; Forsyth, M.; Sun, J. Electrochim. Acta 2003, 48,
2355.
(23) (a) Bennett, M. D.; Leo, D. J. Sens. Actuators A 2004, 115, 79.
(b) Akle, B. J.; Bennett, M. D.; Leo, D. J. Sens. Actuators A 2006, 126,
173.
(24) (a) Fukushima, T.; Asaka, K.; Kosaka, A.; Aida, T. Angew. Chem.,
Int. Ed. 2005, 44, 2410. (b) Mukai, K.; Asaka, K.; Kiyohara, K.; Sugino,
T.; Takeuchi, I.; Fukushima, T.; Aida, T. Electrochim. Acta 2008, 53,
5555.
(25) (a) Bara, J. E.; Camper, D. E.; Gin, D. L.; Noble, R. D. Acc.
Chem. Res. 2010, 43, 152. (b) Bara, J. E.; Hatakeyama, E. S.; Gabriel,
C. J.; Zeng, X.; Lessmann, S.; Noble, R. D. J. Membr. Sci. 2008, 316,
186.
(7) Watanabe, M.; Yamada,, S.-I.; Sanui, K.; Ogata, N. J. Chem. Soc.,
Chem. Commun. 1993, 929.
(8) (a) Noda, A.; Watanabe, M. Electrochim. Acta 2000, 45, 1265.
(b) Susan, M. A. B. H.; Kaneko, T.; Noda, A.; Watanabe, M. J. Am.
408
dx.doi.org/10.1021/ma2022138 | Macromolecules 2012, 45, 401−409

Macromolecules
Article
(26) Scott, K.; Basov, N.; Jachuck, R.; Winterton, N.; Cooper, A.;
Davies, C. Chem. Eng. Res. Des. 2005, 83, 1179.
(48) Wang, C. S.; Zhang, X. B.; Yang, H. S.; Qi, Z. F.; He, P. M.; Li,
W. Z. J. Electrochem. Soc. 1999, 146, 1696.
(27) (a) Lee, J.; Panzer, M. J.; He, Y.; Lodge, T. P.; Frisbie, C. D. J.
Am. Chem. Soc. 2007, 129, 4532. (b) Cho, J. H.; Lee, J.; Xia, Y.; Kim,
B.; He, Y.; Renn, M. J.; Lodge, T. P.; Frisbie, C. D. Nat. Mater. 2008, 7,
900. (c) Lee, J.; Kaake., L. G.; Cho, J. H.; Zhu, X.-Y.; Lodge, T. P.;
Frisbie, C. D. J. Phys. Chem. C 2009, 113, 8972.
NOTE ADDED AFTER ASAP PUBLICATION
■
This article was published ASAP on December 15, 2001. Due
to a production error, various revisions to Table 1, equations,
and several places throughout the text were not present. The
correct version posted on December 22, 2011.
(28) Electroactive Polymer (EAP) Actuators as Artificial Muscles; Bar-
Cohen, Y., Ed.; SPIE Press: Bellingham, WA, 2001.
(29) Pelrine, R.; Kombluh, R.; Pei, Q.; Joseph, J. Science 2000, 287,
836.
(30) (a) Asaka, K.; Oguro, K.; Nishimura, Y.; Mizuhata, M.;
Takenaka, H. Polym. J. 1995, 27, 436. (b) Shahinpoor, M. Electrochim.
Acta 2003, 48, 2343.
(31) (a) Kaneto, K.; Kaneko, M.; Min, Y.; MacDiarmid, A. G. Synth.
Met. 1995, 71, 2211. (b) Baughman, R. H. Synth. Met. 1996, 78, 339.
(c) Smela, E. Adv. Mater. 2003, 15, 48.
(32) Osada, Y.; Okuzaki, H.; Hori, H. Nature 1992, 355, 242.
(33) (a) Takeuchi, I.; Asaka, K.; Kiyohara, K.; Sugino, T.; Terasawa,
N.; Mukai, K.; Shiraishi, S. Carbon 2009, 47, 1373. (b) Takeuchi, I.;
Asaka, K.; Kiyohara, K.; Sugino, T.; Terasawa, N.; Mukai, K.;
Fukushima, T.; Aida, T. Electrochim. Acta 2009, 54, 1762. (c) Terasawa,
N.; Takeuchi, I.; Matsumoto, H. Sens. Actuators, B 2009, 139, 624.
(d) Terasawa, N.; Takeuchi, I.; Matsumoto, H.; Mukai, K.; Asaka, K.
Sens. Actuators B 2011, 156, 539. (e) Lee, J.-W.; Yoo, Y.-T. Sens.
Actuators B 2009, 137, 539.
(34) (a) Wang, J.-S.; Matyjaszewski, K. Macromolecules 1995, 28,
7901. (b) Matyjaszewski, K.; Xia, J. Chem. Rev. 2001, 101, 2921.
(c) Matyjaswewski, K.; Tsarevsky, N. V. Nat. Chem. 2009, 1, 276.
(d) Tsarevsky, N. V.; Matyjaszewski, K. Chem. Rev. 2007, 107, 2270.
(e) Patten, T. E.; Xia, J.; Abernathy, T.; Matyjaszewski, K. Science
1996, 272, 866.
(35) (a) Kato, M.; Kamigaito, M.; Sawamoto, M.; Higashimura, T.
Macromolecules 1995, 28, 1721. (b) Kamigaito, M.; Ando, T.;
Sawamoto, M. Chem. Rev. 2001, 101, 3689.
(36) Ueki, T.; Karino, T.; Kobayashi, Y.; Shibayama, M.; Watanabe,
M. J. Phys. Chem. B. 2007, 111, 4750.
(37) Baughman, R. H.; Cui, C.; Zakhidov, A. A.; Iqbal, Z.; Barisci, J.
N.; Spinks, G. M.; Wallace, G. G.; Mazzoldi, A.; Rossi, D. D.; Rinzler,
A. G.; Jaschinski, O.; Roth, S.; Kertesz, M. Science 1999, 284, 1340.
(38) (a) Nanjo, S.; Watanabe, M.; Asai, K.; Yokoyama, K.;
Yamamoto, M. Abst. 71st Annu. Meet. Electrochem. Soc. Jpn. 2004,
263. (b) Okuno, T.; Sugoh, N.; Kato, T.; Ohgi, H.; Watanabe, M. PCT
Int. Appl. WO2008123064, 2008.
(39) Bonho
̂
te, P.; Dias, A.-P.; Papageorgiou, N.; Kalyanasundaram,
K.; Gratzel, M. Inorg. Chem. 1996, 35, 1168.
̈
(40) Karanam, S.; Goossens, H.; Klumperman, B.; Lemstra, P.
Macromolecules 2003, 36, 3051.
(41) Santangelo, P. G.; Roland, C. M. Macromolecules 1998, 31, 4581.
(42) Mok, M. M.; Liu, X.; Bai, Z.; Lei, Y.; Lodge, T. P.
Macromolecules 2011, 44, 1016.
(43) Bates, F. S. Science 1991, 251, 898.
(44) Jannasch, P. Polymer 2002, 43, 6449.
(45) (a) Tokuda, H.; Tsuzuki, S.; Susan, M. A. B. H.; Hayamizu, K.;
Watanabe, M. J. Phys. Chem. B 2006, 110, 19593. (b) Ueno, K.;
Tokuda, H.; Watanabe, M. Phys. Chem. Chem. Phys. 2010, 12, 1649.
(46) (a) Palmre, V.; Brandell, D.; Maeorg, U.; Torop, J.; Volobujeva,
̈
O.; Punning, A.; Johanson, U.; Kruusmaa, M.; Aabloo, A. Smart Mater.
Struct. 2009, 18, 095028. (b) Torop, J.; Palmre, V.; Arulepp, M.;
Sugino, T.; Asaka, K.; Aabloo, A. Carbon 2011, 49, 3113. (c) Terasawa,
N.; Takeuchi, I. Sens. Actuators B 2010, 145, 775.
(47) (a) Noda, A.; Hayamizu, K.; Watanabe, M. J. Phys. Chem. B
2001, 105, 4603. (b) Tokuda, H.; Hayamizu, K.; Ishii, K.; Susan, M. A.
B. H.; Watanabe, M. J. Phys. Chem B 2004, 108, 16593. (c) Tokuda,
H.; Hayamizu, K.; Ishii, K.; Susan, M. A. B. H.; Watanabe, M. J. Phys.
Chem B 2005, 109, 6103. (d) Tokuda, H.; Ishii, K.; Susan, M. A. B. H.;
Tsuzuki, S.; Hayamizu, K.; Watanabe, M. J. Phys. Chem. B 2006, 110,
2833. (e) Tsuzuki, S.; Shinoda, W.; Saito, H.; Mikami, M.; Tokuda, H.;
Watanabe, M. J. Phys. Chem. B 2009, 113, 10641.
409
dx.doi.org/10.1021/ma2022138 | Macromolecules 2012, 45, 401−409