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Wetting and contact line propagation on solid surfaces
John M. Kolinski, EMSI, EPFL, Lausanne Switzerland
The propagation of a contact line at the interface between liquid and a dry solid is of great fundamental and practical importance. We experimentally probe the dynamics of wetting that occur when an impacting drop first contacts a dry surface. We show that the liquid-solid contact line propagates outward from nanoscale liquid bridges. As the liquid bridge expands, the liquid-air interface deforms and lifts away from the surface immediately ahead of the liquid-solid contact line. The wetting front advances at a velocity well below the liquid capillary velocity ; we explain this anomalously low velocity using a simple model for the interaction between the liquid and the air motivated by the observed liquid-air interface kinematics. As we increase the liquid viscosity, the contact line velocity decreases. A simple boundary layer argument can explain the scaling of contact line velocity as v^-1/3. These results suggest interesting avenues for further study of dynamic wetting on a variety of substrates.