Reconfigurable and Weldable Visible-Light-Driven Liquid-Crystalline Actuators with Enhanced Dynamic Performance

Abstract

A visible-light-driven photoactuator possessing azobenzene moieties and disulfide linkages was prepared with disulfide-containing diacrylate mesogenic oligomers through photopolymerization with azobenzene diacrylate as a cross-linker. Synthesis of mesogenic oligomers with reactive bis(2-hydroxyethyl) disulfide acrylate (ABES) enabled controlled and judicious inclusion of dynamic exchangeable bonding (DEB) in the structure as opposed to traditional postpolymerization oxidative coupling (POC) of thiol groups in liquid-crystalline elastomers (LCEs). This strategy allowed for better control of director alignment, reprogramming ability, and faster self-healing ability through the dynamic exchange reaction (DER). The approach in this work wherein stimuli for actuation and DER were orthogonal overcame drawbacks of the traditional thermally active LCE vitrimers. The prepared monodomain MLCE demonstrated the ability to undergo DER at relatively moderate temperature (∼90 °C), self-healing, multiple reprogramming, and photothermal actuation under blue and ultraviolet (UV) lights. This visible-light-induced shape deformation paves the way for the design of actuators for biomedical applications. Taking advantage of the dynamic nature of disulfide chemistry, the bilayer actuators capable of thermo-or photocontrollable bending/unbending actuation motions were fabricated by welding an MLCE film with azobenzene moieties on a film without azobenzene moieties, via a "glue-free" method through DER. The developed bilayer MLCE films respond to heat and light stimuli and can be used in robotics, health care, and consumer-goods applications such as microrobots, untethered biomimetic grippers, and surgical devices.