Fabricating liquid crystal actuators: from small pre-strain to large actuation strain

Abstract

Liquid crystal elastomers (LCEs) are emerging as compelling materials for soft actuators, sensors, and artificial muscles, due to their reversible and anisotropic deformation upon external stimuli. Incorporating dynamic covalent bonds into LCE networks (xLCEs) introduces reconfigurability and enables programmable actuation through stimuli-activated reversible bond exchange reactions. However, traditional programming approaches typically require large pre-strains at elevated temperatures to induce sufficient mesogen orientation and network rearrangement for large actuation strains, which imposes significant processing constraints. Here, we report an efficient method to fabricate monodomain xLCE actuators with large actuation strains using small pre-strains (as low as 10%). By tuning thermal programming parameters such as temperature and time, we demonstrate that high and tunable actuation can be achieved through the cooperative orientation of mesogens and network rearrangement via bond exchange. Comparative studies with non-liquid crystalline dynamic polymer networks and LCEs without dynamic covalent bond exchange allow us to further understand how large actuation strain can be accessed under minimal mechanical deformation. Moreover, spatial programming of actuation strain is realized by local control over bond exchange kinetics, enabling complex and heterogeneous deformation modes within a monolithic xLCE film.