Dynamics of thin free liquid films stabilized with ionic surfactants

Abstract

To study the dynamics of free liquid films which are stabilized with ionic surfactants, an electrohydrodynamic theory is developed. The long-range interaction forces, namely the repulsive force arising from the overlap of diffuse electric double layers and the attractive Van der Waals-London force, are described by the Maxwell stress tensor with its related field equations and the Van der Waals potential. The short-range surface force has a normal Laplace component and a tangential surface tension gradient component. The total set of first-order equations and their boundary conditions, which describes the capillary waves on the surfaces and the induced flow motion in the film, has been solved. The dispersion relation for the “squeezing mode” is obtained. The cases of no-slip condition and the long-wavelength limit have been studied in more detail. The testability of the dispersion relation using laser beat spectroscopy is reported.