Ion‐Conducting Non‐Flammable Liquid Crystal–Polymer Composites for High‐Frequency Soft Actuators

Abstract

AbstractHigh‐frequency actuators are reported based on non‐flammable lithium‐ion conducting phosphate liquid crystal–polymer composite electrolytes, which exhibit a bending response at frequencies up to 80 Hz under an AC voltage of 2 V, owing to its high ionic conductivity reaching 10−4 S cm−1 at room temperature. An equimolar complex of a phosphate‐containing mesogenic molecule and lithium bis(trifluoromethylsulfonyl)imide through the ion‐dipole interactions induced a room‐temperature smectic A liquid‐crystalline (LC) phase forming 2D ion‐transport pathways comprising the 2D array of the phosphate moieties. A blend of 80 wt% LC electrolyte and 20 wt% polymers (poly(vinyl chloride) and poly(vinylidene fluoride‐co‐hexafluoropropylene)) formed a flexible, mechanically robust LC–polymer composite film. Scanning electron microscopy and white light interference microscopy revealed a microphase‐segregated structure consisting of a continuous LC phase and a porous polymer matrix. In addition, the continuity of porous structure across the film is confirmed by permeation experiments of solvents thorough the membrane with a homemade filter in a dead‐end filtration mode. The LC–polymer composite film sandwiched between two poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid) electrodes is found to simultaneously exhibit high bending strain (0.63%) and high output force (0.35 mN), owing to the high ion migration into the composite electrolyte and electrode.