Characteristics of self-propelled Leidenfrost droplets on asymmetrically structured surfaces: Evidence for a self-rotation-induced propulsive mechanism

Self-propelled Leidenfrost droplets on asymmetrically structured surfaces were investigated to study their movements with temperature. It was observed that the terminal velocity is a function of temperature in the low-temperature regime (L regime) but not in the high-temperature regime (H regime). Droplets were not smooth in the L regime but were smooth in the H regime. Because of wrinkles, the light penetrating through droplets was deflected, resulting in differences in light levels in the L and H regimes. While the droplet accelerated to reach its terminal velocity when α = 50° and α = 65°, tiny droplets were breaking off from the trailing edge and moving opposite to the droplet’s moving direction. When α = 80°, as the droplet accelerated, it leaned forward and its leading edge stood higher than its trailing edge. The distinct shape of the droplet is strong evidence to show that the vapor underneath the droplet flows opposite to the droplet’s moving direction.