ABSTRACT
We turn now to thin films for which one boundary is a free surface between two immiscible liquids. This situation is commonly encountered in nature (gravity currents, spreading of pollution, eye tear film, etc) or in industry (coating of a surface). The hydrodynamics are then often coupled to heat and mass transport phenomena which modify the physical properties of the flowing fluid. For example, the viscosity of lava increases as it cools down. Similarly, the surface tension and viscosity of a paint film change as the solvent evaporates. Such transport phenomena complicate the analysis of the flow and numerical models are usually necessary.
