Vanishing in thin air: drop-bath impacts in reduced pressure

When a liquid drop impacts a bath of the same fluid, it may bounce, coalesce, or transiently float. Under standard atmospheric conditions, the outcome for a particular fluid is governed by the drop’s impact velocity and size, via the Weber number We and Bond number Bo, respectively. In this talk, we present experiments performed in rarefied air that reveal the critical influence of ambient pressure on the outcome of drop–bath impacts. Through controlled sweeps of We, Bo, and air pressure P, we comprehensively map out the transitions between the different behaviors. In particular, we find a minimum drop size required for rebound, which increases as P decreases. Finally, we directly compare our experimental findings to predictions from a computational model that incorporates nanoscale gas-kinetic and disjoining pressure effects in a lubrication model for the air-layer evolution.