Dynamics of partial wetting

Abstract

Two broad classes of models have been used to describe the motion of a contact line when the contact angle θ deviates from the equilibrium value θ e : a) an Eyring approach, emphasizing the microscopic jump of a single molecule at the tip. b) a hydrodynamic approach, concentrating on the viscous losses inside the liquid wedge of angle θ. In the present review, we compare the predictions from both models, for two critical experiments: 1) The pull out of a vertical plate from a fluid at rest -showing (for finite θ e) a critical velocity V c above which the plate is completely wet. 2) The velocity of growth of a dry patch for a non wettable surface covered by a flat liquid film -which turns out to vary like θ e 3 at small θ e. The net conclusion is that, at small θ e and for low velocities V, the hydrodynamic losses dominate, while at large θ e and large V, the molecular features are probably important.