Energy Dissipation and Electromechanical Response in Dielectric Actuation of Liquid Crystal Elastomers

Abstract

Dielectric liquid crystal elastomer actuators (DLCEAs) offer a promising route to low-density actuators with directional control and high power density. Improving the strain response of DLCEAs relative to traditional dielectric elastomer actuators (DEAs) remains an important step toward their use in functional applications such as robotics. Classical DEA theory predicts that strain should scale with the dielectric constant of the active material. Guided by this framework, we prepared and investigated a series of monodomain aligned liquid crystal elastomers (LCEs based on a common liquid crystalline monomer copolymerized with a range of high-dielectric comonomers. These compositional modifications increased the dielectric constant by more than fifty percent; however, DLCEA actuation did not yield the expected increase in strain. To understand this discrepancy, we performed extensive mechanical and dielectric characterization to identify factors suppressing the electromechanical response. Despite increases in dielectric constant, overlap of the mechanical loss peak with the actuation temperature emerges as a dominant dissipation pathway that limits electromechanical transduction. In addition, dielectric losses associated with conductive mechanisms further suppress actuation. Consistent with these findings, DLCEAs combining high dielectric constant with high mechanical loss require extended time scales to approach equilibrium strain. Compared to conventional DEA materials, LCEs exhibit both larger magnitudes and distinct modes of dissipation, which can amplify the role of loss in limiting DLCEA electromechanical performance.