Rebound dynamics of inverse Leidenfrost droplets on dry ice surfaces

In this paper, we experimentally investigate the rebound dynamics of droplets on dry ice surfaces, unveiling the mechanism behind the inverse Leidenfrost phenomenon. We demonstrated that the underlying mechanism driving the inverse Leidenfrost phenomenon is the lift force from the air film generated by the sublimation of dry ice. The air film prevents droplet condensation, facilitating the droplet rebound. However, the presence of film significantly depends on impact conditions. During the early spreading stage, bubbles nucleate at the contact line due to the sublimation, then the bubbles grow and gradually form an air film. We showed that the droplet rebound occurs only when the air film fully forms before the maximum spreading stage. Otherwise, the contact line is frozen, ultimately preventing rebound. We propose a theoretical expression of critical air film thickness that determines whether the droplet rebounds. Based on the expression, we ultimately established a theoretical criterion for droplet rebound via thermodynamic and fluid dynamics principles. To validate our developed theoretical criterion, we further investigated the inverse Leidenfrost phenomenon for different fluids, Weber numbers, and different temperatures of droplets. The results demonstrate a high consistency between the predicted results of our theoretical criterion and experimental results.