Enhanced Actuation Stability of Liquid Crystal Elastomer Actuators With Diels-Alder Dynamic Bonds

Polymeric materials capable of undergoing reversible shape change can be used as soft actuators to create low-density, compliant machines. Liquid crystal elastomers (LCEs) are a promising class of soft actuators that undergo large, reversible shape change by heating and cooling, but the fabrication of these materials requires molecular alignment to be trapped by crosslinking. LCEs with dynamic crosslinks can dramatically simplify materials processing and allow for reprogramming of the material after synthesis. However, thermally labile dynamic crosslinks can break during actuation, leading to a degradation of actuator performance over time. Herein, we developed LCEs with dynamic crosslinks with well-separated actuation and processing temperature regimes. Diels-Alder (DA) crosslinks based on 3-substituted furans are more thermally stable, achieving an actuation strain of 35.2% ± 0.5% and an actuation stress of 213.7 ± 20.1 kPa. These values are higher than those obtained from DA bonds formed with 2-substituted furans, which have been commonly used in LCE systems with DA crosslinks. The introduction of 3-substituted furan allowed reversible actuation and improved thermal stability relative to 2-substituted furan, while maintaining reprogrammability and reprocessability. We leverage the combination of thermal stability and facile reprocessability to create multiple, dynamic diffraction gratings in a single material.