Thermally Gated Covalent Adaptivity in Liquid Crystal Elastomers for Stable Actuation.

Abstract

Liquid crystal elastomers (LCEs), with reversible actuation of large and anisotropic deformation, have surged in smart materials such as soft robotics, sensors and artificial muscles. LCEs incorporating dynamic covalent bonds (DCBs) endowing network with rearranging ability through reversible bond reaction, facilitating the fabrication of soft actuators with tailored actuation modes and reprogrammability. However, unintended activation of DCBs during actuation, particularly under thermal perturbations, remains a critical challenge, as it damages actuation stability which arises catastrophic failure and potential security risks in practical applications. Present strategies in enhancing actuation stability either achieve only temporary stability or sacrificed reprogrammability or actuation performance. Here, we propose a strategy incorporating catalyst-free α-AC/A DCB of high temperature active-threshold to fabricate stable dynamic LCE actuators with thermally gated behavior. This design exhibits a "thermal gate" at 120 °C with inert bond exchange below this threshold, yet rapidly activated at 160 °C. The integrated permanent crosslinks further prevent unintended chain slippage, ensuring topological stability. The resulting dynamic LCE could be fabricated to actuators efficiently and exhibiting unprecedented durability at 120 °C (sustaining 10,000 actuation cycles). The switches between reprogrammability and actuation stability are long-standing reversible, meeting the demands of long-term service without compromising its reprogrammability.