Bouncing drops on a vibrating solid: Air film dynamics in the ‘bound’ and ‘bouncing’ states

Previous observations have been made of ‘perpetual’ drop rebound on a vibrating bath of viscous liquid. We here report the experimental observation of a prolonged bouncing state on a solid sheet of atomically smooth mica vibrated at frequency f. By varying f, we produce a resonance curve for the drop’s amplitude and observe a sharp transition at a critical frequency f_c from a ‘bouncing’ state – where a significant air gap is observed between the drop and the vibrating sheet – to a ‘bound’ state, where the drop does not make contact, but remains in close proximity to the solid for prolonged periods. We use axisymmetric volume-of-fluid simulations to explore the phase space and find that the ‘bouncing-to-bound’ transition is robust and depends on drop size and forcing amplitude. Using two-color interferometry, we characterize the air film dynamics below the drop and discuss the mechanism for the transition from a bouncing to a bound state.