Air film contact modes of drop impact on lubricated surfaces under reduced pressures

Air film evolution underneath a drop impacting on a surface can cause the drop to either bounce off or make contact. Water drops impacting on a dry surface exhibited a transition from bouncing to the kink and film modes of contact. Additionally, a dimple mode of contact was observed on a lubricated, smooth surface. Here, we report experimental findings of drops impacting on a lubricated, smooth surface under both reduced and atmospheric pressures using liquids of two different viscosities. The kink mode observed on a dry surface only occurs at low impact velocities under reduced pressures but is completely absent at the atmospheric pressure on a lubricated surface. The horizontal extent of the dimple agrees well with the incompressible and compressible scaling within the inertial regime. The experimentally measured horizontal extent of the kink shows good agreement with the existing theoretical scaling. Slight deviations in the contact mode transition were observed between experiments and previously reported simulations, presumably due to the velocity slip at the air-lubricant interface in the present study.