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

High-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.