Bouncing drop on liquid film: Dynamics of interfacial gas layer

The transition between merging and bouncing outcomes for a drop impacting on a liquid film is critically controlled by the resistance from the microscopic interfacial gas layer trapped between the interacting and deformable drop and film surfaces. Using high-speed imaging and color interferometry, we have quantified and analyzed the gas layer dynamics during bouncing when the liquid film thickness is comparable to the drop radius. Results show that the gas layer morphology changes dramatically and non-monotonically with the film thickness and that in addition to the centrally located dimple previously observed for impact on thin films, a new, rim-dimple morphology is observed for larger film thicknesses. The effects of capillarity of the drop and film are also delineated by increasing the liquid viscosity and hence damping the respective surface waves.