Air plastron–enabled heat management for enhanced photothermal actuation in underwater soft robots

Photothermal self-excited actuators, offering untethered power and control, are promising for autonomous soft robots. While most efforts focus on enhancing heat absorption for greater actuation performance, managing heat dissipation remains underexplored, which becomes critical in underwater environments with rapid convective cooling. Inspired by amphibious mammals that use air plastrons for thermal insulation, we develop a strategy incorporating superhydrophobic candle soot coating to trap air on photothermal liquid crystal elastomer (LCE) actuators. This approach substantially improves thermal insulation underwater, enhances internal temperature gradient, and causes a 282-fold increase in calculated work output. Moreover, we reveal a previously unreported self-oscillation mechanism based on total internal reflection enabled by air plastron, which decouples the locomotion direction from the light incidence direction. Leveraging the enhanced output and maneuverability, we demonstrate LCE-based robots capable of self-continuous locomotion underwater and on water surfaces, powered by overhead or horizontal light, paving the way for next-generation untethered high-performance aquatic soft robots.