Coupled flow phenomena in thin free-surface films

The flow of aqueous salt solutions in thin free-surface films is analyzed with a simple physico-chemical model. In addition to gravity, gradients in temperature, solute concentration and electric potential act as forces on the film. Through surface-tension gradients, electro-kinetic effects and thermal diffusion, a non-equilibrium thermodynamic coupling between the four forces and their respective fluxes is established. A global treatment of the Onsager thermodynamics is used to describe the cross-coupling, the physicochemical model used is shown to satisfy the Onsager reciprocal theorem and the relative importance of the various surface phenomena occurring in the film is acessed.