Evaporation Preempts Complete Wetting

A volatile liquid wetting a substrate forms a thick, uniform film in equilibrium with a saturated vapor phase. We show that under evaporating conditions such a liquid is effectively non-wetting, i.e. stable as a droplet on top of a thin film. This is in agreement with recent observations. Here we calculate the contact angle of the droplet as a function of the liquid-vapor surface tension and the partial pressure. This effect will be useful as a means of probing the microscopic interfacial forces involved in wetting via macroscopic measurements.