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 dependence of the surface diffusion coefficient of the adsorbed surfactant molecules on the density of the adsorption layer. The analysis shows that the Gibbs elasticity disappears from the final equations describing the drainage and hydrodynamic stability of thin liquid films. Thus from a theoretical viewpoint, no correlation between the Gibbs elasticity and the dynamic properties of the thin foam and emulsion films is expected. This conclusion is valid also for a variety of other dynamic processes (in a quasi-stationary regime) where the concentration Marangoni effect is important, such as the motion of drops and bubbles in a liquid medium, and rheology of foams and emulsions. 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.