Mesophase Tunable Actuation of Ionic Thiol-Acrylate Liquid Crystal Elastomers

Electroactive polymers (EAPs) are envisioned to play a crucial role in next-generation soft robotics for their lightness, compliance, and high degree of actuation freedom. Among many, ionic EAPs (IEAPs) have gained traction due to their low driving voltages. However, they suffer from drawbacks like difficulty in programming microstructure and actuation behavior. Ionic liquid crystal elastomers (iLCEs) are introduced as a new class of IEAPs to address such issues thanks to their programmable anisotropic molecular structure. Herein, the repertoire of iLCEs by synthesizing electroactive thiol-acrylate iLCEs with tailorable microstructure and actuation behavior is expanded, and the effect of iLCEs' mesophase on their microstructure and actuation is studied. Low-frequency impedance analysis was utilized as a powerful tool to elaborate on the ionic migration and interfacial polarization of iLCEs, which show correlation to the electric actuation. It was found that thiol-acrylate iLCEs experience Maxwell-Wagner-Sillars (MWS) relaxations. The mesophase (nematic or smectic) and genesis (monodomain or polydomain) impact the actuation behavior by affecting the time scale required for the accumulation of ions at interfaces. These correlations are consistent with underlying ion migration pathways and indicate that monodomain alignment enables prolonged interfacial polarization and improved actuation, while the cybotactic smectic phase provides additional ion-accumulation dynamics.