Robust and Reprocessable Artificial Muscles Based on Liquid Crystal Elastomers with Dynamic Thiourea Bonds

This work reports a new class of liquid crystal elastomers (LCEs) cross-linked with poly(ether-thiourea) comprising a triethylene glycol spacer (LCE-TUEG) wherein thiourea bonds impart a hydrogen bonding capability as well as permit dynamic covalent bond (DCB) exchange at elevated temperatures. While hydrogen bonding enhances the mechanical properties of LCE-TUEG, the DCB allows the macromolecular network rearrangement of the LCEs, resulting in various useful properties that are not present in conventional LCEs, including the ability to undergo welding, melt and solution reprocessing, reprogrammable actuation, and self-healing. By exploiting these dynamic features, electrically powered artificial muscles are fabricated that can be actuated by Joule heating using a resistive wire. In particular, an excellent specific work is demonstrated (approximate to 65 J kg(-1)) for the artificial muscle, and full recyclability of both the LCE matrix and the metallic heating wire is achieved. Furthermore, a biomimetic artificial hand is created by welding and assembling multiple LCE-TUEG films embedded with heating wires, followed by mechanical alignment. The integration of a microcontroller to the artificial hand enables the selective actuation of each finger, and various hand gestures are successfully demonstrated.