EVAPORATION PREEMPTS COMPLETE WETTING

volatile liquid wetting a substrate forms a thick, uniform film in equ ilibrium 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 observ ations. Here we calculate the contact angle of the droplet as a functi on of the liquid-vapor surface tension and the partial pressure. This effect will be useful as a means of probing the microscopic interfacia l forces involved in wetting via macroscopic measurements.