Thermomechanically Active Electrodes Power Work-Dense Soft Actuators*

We studied the effect of chain extender structure and composition on the thermomechanical properties of liquid crystal elastomers (LCE). The molecular stiffness of the thiol chain extender and its relative molar ratio to acrylate-based host mesogens determine the thermomechanical strains, transition temperatures and the mechanical work-content. Higher concentrations of flexible extenders first magnify the thermomechanical sensitivity, but a continued increase leads to weaker actuation. This study leads to a composite material platform that achieves a peak specific work of ~2 J/kg using ~115 mW of electrical power. Composites of LCE with eGaIn liquid metal (LM) are prepared, which act both as heaters and actuators. The thermomechanically active electrodes actuate by Joule heat and efficiently couple with the neat LCE to which they are bound. This system harnesses the nascent responsiveness of the LCE using collaborative electrodes. Specific work generated by the composite actuators increases with load until ~260x their weight. These ideas are extended to tri-layered actuators, where LCE films with orthogonal molecular orientations sandwich LCE-LM composite heaters, harnessing torsional actuation modes.