Role of surface diffusion for the drainage and hydrodynamic stability of thin liquid films

The dynamics of thin liquid films is analyzed taking into account the depen dence of the surface diffusion coefficient of the adsorbed surfactant molec ules on the density of the adsorption layer. The analysis shows that the Gi bbs elasticity disappears from the final equations describing the drainage and hydrodynamic stability of thin liquid films. Thus from a theoretical vi ewpoint, no correlation between the Gibbs elasticity and the dynamic proper ties of the thin foam and emulsion films is expected. This conclusion is va lid also for a variety of other dynamic processes (in a quasi-stationary re gime) where the concentration Marangoni effect is important, such as the mo tion of drops and bubbles in a liquid medium, and rheology of foams and emu lsions. The theory predicts that the main factors governing these processes are (i) the density of the adsorption layer and (ii) the surface friction coefficient of the adsorbed molecules.