title: Dynamics of collapse of air films in drop impact.
abstract: Liquid drops hitting solid surfaces deform substantially under the influence of the ambient air that needs to be squeezed out before the liquid actually touches the solid. Nanometer- and microsecond-resolved dual wavelength interferometry reveals a complex evolution of the interface between the drop and the gas layer underneath. For intermediate impact speeds (We∼1…10) the layer thickness can develop one or two local minima-reproduced in numerical calculations-that eventually lead to the nucleation of solid-liquid contact at a We-dependent radial position, from a film thickness >200  nm. Solid-liquid contact spreads at a speed involving capillarity, liquid viscosity and inertia.
authors.affiliation: Physics of Complex Fluids, MESA Institute for Nanotechnology, University of Twente, Enschede, The Netherlands.
authors.forename: Jolet
authors.initials: J
authors.lastname: de Ruiter
authors.forename: Jung Min
authors.initials: JM
authors.lastname: Oh
authors.forename: Dirk
authors.initials: D
authors.lastname: van den Ende
authors.forename: Frieder
authors.initials: F
authors.lastname: Mugele