High-performance polymer actuators based on poly(ethylene oxide) and single-walled carbon nanotube–ionic liquid-based gels

The electrochemical and electromechanical properties of actuators based on the polymer electrolyte poly(ethylene oxide) (PEO), fabricated using a single-walled carbon nanotube (SWCNT)-ionic liquid (IL)-based gel electrode, were compared with those of actuators based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF(HFP)).The ionic conductivity of the PEO/IL gel electrolyte layer was much smaller than that of the PVdF(HFP)/IL layer. This is likely because the interaction between the oxygen atoms of PEO and the cations of the IL was larger than that between the fluorine atom of PVdF(HFP) and the IL cations. The maximum strain of the PEO electrolyte layer was smaller than that of the PVdF(HFP) electrolyte layer. Further, the maximum strain of an EMI[TFSI]/PEO electrode-based actuator was approximately 1.3 times larger than that of an EMI[TFSI]/PVdF(HFP) electrode-based actuator, where EMI[TFSI] is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide. These results indicated that the PEO electrode-based actuators exhibited better performances than those based on a PVdF(HFP) electrode.In the case of the PEO electrode-based actuators, it was also found that the ion size, and the self-diffusion coefficient, as well as the rate of ion transport in the electrodes and electrolyte, were of critical importance for realizing low-voltage actuators. Finally, a simple model for the actuation mechanism was also proposed. The model, which was based on the product of the ionic transport number and the ionic volume, was shown to successfully explain the actuator behavior.