Self-Repeatable snapping liquid–crystal-elastomer actuator

• Developed a self-repeatable film-type LCE actuator for continuous self-snapping. • Solved one-time snapping limits of soft actuators by confining reversible LCE films in a frame. • Demonstrated the first organic fire alarm system, preventing metal oxidation and corrosion. • Enabled directionally adjustable crawler-robots using frame-confined LCE film. Liquid crystal elastomers (LCEs) show potential for use in sensors and robotics owing to their reversible stimuli response. However, current actuators have limitations such as low power and slow recovery. Incorporating snap-through transitions induced by mechanical instability into motion can enhance the speed and power of soft actuators. However, the snap-through transitions’ single-shot motion response without external assistance at complicates their application to continuous and self-repeatable actuation. This study introduces a promising and simple approach for creating a rapid and self-repeatedly regulated snapping motion in an LCE actuator by confining the LCE film in a frame. We explore the confinement effect of a freestanding pre-curved LCE film that smoothly changes its bending direction and shows anticlastic buckling. Interestingly, a self-repeating snapping motion is generated by attaching a rigid film onto the LCE film, thereby inducing synclastic deformation. Remarkably, the up-and-down bending snapping motion occurs at a very high speed (within 30 ms) and is self-regulated depending on the temperature of the bottom surface. By utilizing this thermally responsive snapping LCE actuator, we successfully demonstrate an organic-based novel fire alarm and a self-propelled soft-walk mechanism.