Evolution of liquid/solid contact area of a drop impinging on a solid surface

Time evolution of liquid/solid contact area of impacting drop on a solid surface has been investigated experimentally by means of a flash photographic method. The case has been treated where water drops with about 2.4 mm in diameter impinge vertically on a horizontal smooth surface. It has been found that a liquid drop contacts the surface with a ring-shape at the moment of collision. Inside this ring-shaped liquid/solid contact area, air is entrapped between the liquid and the solid surface. Liquid does not contact the surface there. The noncontact area decreases sharply with time, and then becomes constant. The physical phenomena occurring at the liquid/solid interface have been discussed from an experimental point of view.