Damped bouncing of Leidenfrost drops*

When a liquid drop comes in contact with a very hot surface, a continuous vapor layer is formed between the drop and the solid surface, thereby hindering direct liquid-solid contact. This well-known phenomenon is commonly referred to as the Leidenfrost effect. A drop in the Leidenfrost state is highly mobile, and recent studies have shown that pressure perturbations in the vapor layer, arising from ripples at the bottom of the drop, can cause the drop to spontaneously bounce on the substrate as its size reduces to below capillary length due to evaporation. In this work, we show that this bouncing of the Leidenfrost droplets can be damped if the surface is textured with interconnected cavities of length scale comparable to or smaller than the ripple wavelength. We systematically investigate this effect by observing gently deposited Leidenfrost drops on a range of textures of length scale spanning from a few tens to a few hundred micrometers. We show that gently deposited Leidenfrost drops can traverse such surfaces with minimal bouncing and quantify the dynamics of such drops in terms of drop motion and ripples on the drop surface. We also show that disconnected cavities do not lead to suppression of bouncing, thus providing a design criterion for such surfaces.