Temperature-mediated directional self-propulsion of ice blocks on hot ratchet surfaces

The interplay between phase change and surface asymmetry enables remarkable self-propulsion. We report temperature-mediated motion of ice blocks on superheated ratchet surfaces, revealing a three-phase Leidenfrost regime bridging melting and vapor levitation. Below around 400 °C, asymmetric meltwater ejection within the transition-boiling regime drives geometry-dependent bidirectional motion. Above this threshold, a stable vapor-meltwater cushion forms, producing unidirectional propulsion via pressure rectification. The coupling of melting, boiling, and asymmetric confinement extends the Leidenfrost framework to solid–liquid–vapor systems, offering new insight into autonomous thermal transport and self-regulated cooling.