This paper describes the preparation, physical properties, and electric bending actuation of a new class of active materials—ionic liquid crystal elastomers (iLCEs). It is demonstrated that iLCEs can be actuated by low‐frequency AC or DC voltages of less than 1 V. The bending strains of the unoptimized first iLCEs are already comparable to the well‐developed ionic electroactive polymers. Additionally, iLCEs exhibit several novel and superior features, such as the alignment that increases the performance of actuation, the possibility of preprogrammed actuation patterns at the level of the cross‐linking process, and dual (thermal and electric) actuations in hybrid samples. Since liquid crystal elastomers are also sensitive to magnetic fields and can also be light sensitive, iLCEs have far‐reaching potentials toward multiresponsive actuations that may have so far unmatched properties in soft robotics, sensing, and biomedical applications.
The
present article entails the generation of flexoelectricity
during cantilever bending of a solid polymer electrolyte membrane
(PEM), composed of poly(ethylene glycol) diacrylate (PEGDA) precursor
and ionic liquid (hexylmethylimidazolium hexafluorophosphate).
The effects of thiosiloxane modification of PEGDA precursor on glass
transition, ionic conductivity, and flexoelectric performance have
been explored as a function of PEM composition. The glass transition
temperature (T
g) of the PEM declines with
increasing thiosiloxane amount in the PEGDA co-network, while the
ionic conductivity improves. The PEM/compliant carbonaceous electrodes
assemblies were assembled to determine the flexoelectric coefficients
by monitoring electrical voltage/current outputs for various PEM compositions
under the intermittent square-wave and dynamic oscillatory sine-wave
deformation modes. Of particular interest is that the room temperature
flexoelectric coefficient exhibits strong frequency dependence in
the vicinity of 0.01–10 Hz, suggesting that ion polarization
and ion transport through the ion-dipole complexed networks can still
be affected by the mobile side chain branches even in the elastic
regime of the covalently bonded PEGDA network. The in-depth understanding
of the effect of thiosiloxane side chain on flexoelectricity generation
is anticipated to have impact on the development of mechanoelectrical
energy conversion devices for energy harvesting applications from
natural and dynamical environment.
The first study of the flexo-ionic effect, i.e., mechanical deformation-induced electric signal, of the recently discovered ionic liquid crystal elastomers (iLCEs) is reported. The measured flexo-ionic coefficients were found to strongly depend on the director alignment of the iLCE films and can be over 200 µC/m. This value is orders of magnitude higher than the flexo-electric coefficient found in insulating liquid crystals and is comparable to the well-developed ionic polymers (iEAPs). The shortest response times, i.e., the largest bandwidth of the flexo-ionic responses, is achieved in planar alignment, when the director is uniformly parallel to the substrates. These results render high potential for iLCE-based devices for applications in sensors and wearable micropower generators.
Preparation and low voltage induced bending (converse flexoelectricity) of crosslinked poly(ethylene glycol) diacrylate (PEGDA), modified with thiosiloxane (TS) and ionic liquid (1‐hexyl‐3‐methylimidazolium hexafluorophosphate) (IL) are reported. In between 2µm PEDOT:PSS electrodes at 1 V, it provides durable (95% retention under 5000 cycles) and relatively fast (2 s switching time) actuation with the second largest strain observed so far in ionic electro‐active polymers (iEAPs). In between 40 nm gold electrodes under 8 V DC voltage, the film can be completely curled up (270° bending angle) with 6% strain that, to the best of the knowledge, is unpreceded among iEAPs. These results render great potential for the TS/PEGDA/IL based electro‐active actuators for soft robotic applications.
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