Enhanced Actuation Stress in Variable Stiffness Liquid Crystal Elastomers

Abstract

Liquid crystal elastomers (LCEs) are promising candidates for artificial muscles due to their thermo-responsive nematic-to-isotropic transition, which enables high strains at accessible temperatures and mimics the adaptable resting state of natural muscle. However, LCEs have lower force outputs than other soft actuators. This work reports an LCE formulation that achieves a 5× increase in actuation force through mechanical intervention. Incorporating low-melting-point alloy Field's metal (FM) particles into the LCE matrix both enhances actuation stress and introduces tunable stiffness. At low FM concentrations (≤10 vol%), actuation stress increases fivefold due to mechanically enhanced network entropy. At higher concentrations (≈30 vol%), the composite exhibits variable stiffness, behaving metal-like when below the FM's melting point and softening once the FM melts. These formulations not only enhance actuator performance in terms of stress and strain but also mimic muscle-like rheological behavior, advancing LCEs toward practical artificial muscle applications.