Tailoring Diels–Alder Cross-Linked Liquid Crystal Elastomers for Spatially Programmable Monolithic Actuators

Abstract

Liquid crystal elastomers with thermo-reversible Diels-Alder cross-links (DALCEs) offer exceptional reprocessability and mild-temperature reprogrammability, enabling repeated fabrication of diverse actuators. However, optimizing their molecular design and refabrication protocols remains crucial to further unlocking their potential. This work systematically investigates DALCEs synthesized via aza-Michael addition reactions between RM82, furfurylamine, and various chain extenders (phenylethylamine, ethylamine, butylamine, hexylamine, octylamine, and 6-amino-1-hexanol). The effects of cross-linking density and chain extender selection on phase behavior, thermomechanical properties, and actuation performance have been thoroughly examined. The results show that a PEA-based formulation with moderate cross-linking density achieves the most balanced performance. Based on this optimized formulation, a novel (re)fabrication strategy is introduced by harnessing DALCEs' intrinsic reprocessability, reprogrammability, and self-healing properties. This strategy employs multilevel fiber programming before monolithic actuator formation, enabling spatially controlled liquid crystal alignment and facilitating iterative actuator refinement through reconstruction. Consequently, complex morphing behaviors in disk films and stress-modulating functions in tubular actuators were demonstrated. This work establishes a versatile, easily synthesized material platform for spatially programmable, dynamic monolithic actuators, paving the way for advanced applications in soft robotics and adaptive devices.