The effect of double layer interaction on the drainage of thin liquid films

Abstract

The drainage of thin liquid films of an aqueous solution containing anionic surfactant and inorganic electrolyte between platinum and a mercury pool electrode was examined by the capacitance method. The system consisted of either symmetrical or unsymmetrical potentials of diffuse double layers which were estimated by differential capacitance measurements. The results showed that the drainage of the liquid film initially took place quickly and then slowly attained an equilibrium thickness. This general tendency could be explained qualitatively by the theoretically calculated disjoining pressure but the equilibrium thickness of 7–13 nm was too small to be explained in terms of electrostatic repulsion and van der Waals attraction. Hence, it was supposed that other forces, such as steric hindrance, are acting to thicken the film in addition to the above mentioned disjoining pressure. The force acting on the film obtained from the Reynolds equation also indicates the presence of other forces which are acting to thin the film in addition to gravity.