AN EXPERIMENTAL STUDY OF A WATER DROPLET IMPACTING ON A ROTATING WAFER

The evolution of droplet impact is influenced by a moving surface when a free-falling water droplet impacts onto a dry rotating silicon wafer In the early stage of drop impact, the bottom of the liquid drop adheres on the surface and is simultaneously dragged by the moving surface. The remainder of the drop, governed by the force of inertia, remains and expands above the point of impact. There are two important outcomes of impact between the stationary and moving surfaces. First, the deposited film is elongated by a moving surface to form asymmetrical geometry, and the area of deposited film increases to elevate the surface velocity. Second, either detachment or splashing appears in high surface velocity, which is an impossible occurrence in a smooth and stationary surface. When the surface velocity or impingement angle reaches critical value, surface tension on the upper portion of the droplet can be overcome, resulting in droplet breakup; then the liquid starts to detach or splash. The surface velocity increases and the amount of detaching liquid increases accordingly.