ABSTRACT
Interfacial phenomena are also important in other applications involving fluid flow, e.g., microfluidic devices (Stone and Kim, 2001; Tabeling, 2005). In some cases only the shapes of fluid-fluid interfaces need be studied, for instance, in the coating problems. Here, the material to be coated is in the form of a flat plate or wire that is withdrawn continuously from a pool of liquid. The liquid adheres to the surface as a thin film of constant thickness and is dried to form the coating. Considering that the coat thicknesses are very small and that the uniformity of the coat is often essential to the product, there exists a great need for precision (Derjaguin and Levi, 1964; Kistler and Schweizer, 1997). Knowledge of the thickness of the liquid layer (i.e., the shape of the liquid interface) (see Figure 7.3) as it deposits on the solid surface, is needed. This is well known as the dip coating problem. Similar problems where the final products or processes depend on the shapes of moving fluid-fluid interfaces are widely known: in extrusion of polymer melts, in fiber spinning, in formation of droplets from jets, in spreading of ink drops, oil slicks, etc.
