Enhancing electromechanical responsiveness of PVC gels via ion size control

Abstract

Soft electroactive polymer materials are of great interest for soft robotics and biomedical applications because of their large deformability and fast response. Plasticized poly(vinyl chloride) (PVC) gels, particularly PVC/dibutyl adipate (PVC/DBA) gels, exhibit significant bending deformation under relatively low electric fields. In this study, we enhanced the electromechanical response of PVC/DBA gels by adding salts with controlled ion sizes, including ionic liquids and lithium salts. Rheological measurements revealed a critical gelation concentration (PVC weight fraction) of w = 0.013 and a fractal dimension of 1.88. At a fixed PVC concentration (w = 0.143) corresponding to a post-gel state, salt addition (5.4 × 10⁻⁶ mol g⁻¹) increased electrical conductivity by approximately fivefold without significantly affecting elasticity. All gels showed anode-directed bending under an DC electric field, with deformation magnitudes more than five times larger than those of salt-free gels. The most pronounced bending was observed for gels containing a small anion, bis(fluor sulfonyl)imide, and a large cation, 1-ethyl-3-methylimidazolium, which is attributed to asymmetric effective charge densities formed in the electric double layer at the electrodes. These results demonstrate that the ion size control of added salts is an effective strategy for enhancing the electromechanical performance of PVC/DBA gels under low electric fields.