The Interfacial Physics Group

Abstract

By direct microscopic measurements of the meniscus shape in the immediate vicinity of the moving contact line, we quantify the effects of viscous forces on the interface shape. Single parameter fits to the interface shapes predicted by theory give excellent results. The existence of the geometry independent region on the interface has been verified. In analogy to the static contact angle, the interface shape in this geometry independent region forms a well defined characterization of the dynamic wettability of a materials system. We have thus developed and demonstrated an instrument and method for measuring a dynamic contact angle boundary condition. With this technique other measures of dynamic wettability can be properly interpreted and predictive models of spreading can be implemented for the first time. Our results put strong restrictions on the asymptotic functional form of the interface shape predicted by any model which attempts to describe the hydrodynamics occurring on the microscopic scale near a moving contact line. With our methods, the velocity dependence of the parameters which govern the flow in this inner region can be investigated.