Gravitational drainage of a tangentially-immobile thick film

We use lubrication theory to derive an evolution equation for the free surf ace of a draining thick free film with a zero tangential velocity component along the free surface, The films are "thick" because effects that are imp ortant in very thin films, such as intermolecular forces, do not play a rol e in the situation of interest. The evolution equation results from the bal ance of surface tension, gravity, and dynamic viscosity. Subregions of the film appear and they involve balancing these effects pairwise. Computations are performed on the full evolution equation and for various boundary cond itions corresponding to different parts of the film. Matched asymptotics ar e developed that predict the behavior as the film enters the bath and these agree very well with the computed results. Comparison with experiment is f avorable for the rate of decrease of the film thickness. (C) 1999 Academic Press.