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 ~ 400 {degree sign}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 insights into autonomous thermal transport and self-regulated cooling.