Singularity and jet formation for drop impact on a dry surface*

We study the influence of the surrounding gas in the dynamics of drop impact on a smooth surface. We use a model for which both the gas and the liquid are incompressible; lubrication regime applies for the gas film dynamics and the liquid viscosity is neglected. We show that in the absence of surface tension a singularity is formed when the liquid touches the solid, while a thin film of air always remains present between the solid and the liquid when surface tension is taken into account. We explain the self-similar structure of the singularity and we show that the jet thickness is proportional to the capillary length of the impact.