Dynamics of partial wetting

Abstract

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 θe : 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 θe) a critical velocity Vc 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 θe3 at small θe. The net conclusion is that, at small θe and for low velocities V, the hydrodynamic losses dominate, while at large θe and large V, the molecular features are probably important.