Electrohydrodynamics of thin free liquid films stabilized with ionic surfactants

Abstract

To describe the dynamics of thin free liquid films which are stabilized with ionic surfactants, an electrohydrodynamic theory has been recently developed. The long-range interaction forces, namely the electrodynamic interaction between the ions and the van der Waals-London attraction amongst all molecules, are described by the Maxwell stress tensor and the van der Waals-potential in the hydrodynamic equations of motion, which are now coupled with the field equations. The surface force exerted on the adsorbed charged boundary monolayers has a normal Laplace component and a tangential surface tension gradient component. The “stretching mode” which is responsible for the high frequency behavior of the films, has been studied, and the case of no-slip condition in the long-wavelength limit has been treated in more detail. It seems that our new predictions are confirmed experimentally. Finally, the dynamic stability of such films is discussed in the light of this theory.