Air Plastron–Enabled Heat Management for Enhanced Photothermal Actuation in Underwater Soft Robots

This study introduces an air-plastron–enabled thermal-management strategy that dramatically enhances photothermal actuation of liquid crystal elastomer (LCE) soft robots operating underwater. A superhydrophobic candle-soot coating traps a persistent air layer on the actuator surface, substantially suppressing convective heat loss and enabling a large temperature gradient across the LCE thickness—even in highly dissipative aqueous environments. Experiments show a 282-fold increase in calculated work output relative to uncoated LCE actuators, driven by larger thermally induced strain differentials. The authors also discover a previously unreported total-internal-reflection (TIR)–based feedback mechanism that enables stable self-oscillation without requiring alignment between the light source and motion direction. With this enhanced thermal gradient and TIR-enabled decoupled actuation, coated LCE robots achieve sustained underwater locomotion, interface-swimming, and overhead-illumination–driven motion. These findings establish a new materials-engineering route for untethered, high-performance aquatic soft robots.