Size-dependent spontaneous oscillations of Leidenfrost droplets

A liquid droplet hovering on a hot solid surface is commonly referred to as a Leidenfrost droplet. In this study, we discover that a Leidenfrost droplet spontaneously performs a series of distinct oscillations as it shrinks during the span of its life. The oscillation first starts out erratically, followed by a stage with stable frequencies, and finally turns into periodic bouncing with signatures of a parametric oscillation and occasional resonances. The last bouncing stage exhibits nearly perfect collisions. We showed experimentally and theoretically the enabling effects of each oscillation mode and how the droplet switches between such modes. We finally show that these spontaneous oscillation modes and the conditions for transitioning between modes are universal for all tested combinations of liquids and surfaces.