Novel Flame-Actuated Soft Actuator Based on a Multilayer Liquid Crystal Elastomer/Hydrogel Composite

A novel flame-actuated soft actuator based on a multilayer liquid crystal elastomer/hydrogel composite was fabricated in this work. Flame is a preferable external stimulus over light, heat, and electricity in terms of its abundant accessibility in a fire scenario. Nevertheless, employing flame as the external stimulus introduces novel challenges for soft actuator materials as they must possess incombustible properties. Here, hydrogel layers are grafted on both surfaces of the liquid crystal elastomer (LCE), resulting in the fabrication of a trilayered LCE-hydrogel composite. The LCE-hydrogel composite demonstrates remarkable flame retardancy, shape memory performance, and tailorable surface adhesion. The hydrogel’s remarkable water absorption and heat insulation properties confer excellent flame retardancy to the composite, preventing ignition for at least 10 s during the open flame test. The shape memory performance is attributed to the orientation of the internal LCE layer and the flexibility of the external hydrogel layers. The surface adhesion of the hydrogel layers is tailored by adjusting their water content. As the water content decreases from 100 to 60%, the surface adhesion energy increases from 6.2 to 70.3 J/m2. A flame-actuated, clip-like soft robot capable of cyclically grasping and releasing objects was constructed, showcasing its promising application potential. This work presents an unprecedented flame-actuated LCE-based composite for the first time, which offers a fresh perspective for researchers to investigate alternative actuation approaches in the field of soft robotics.