Surface charging mechanism for electrolytic soap films
CNRS, Laboratoire de Physique Théorique de l'ENS,
24 rue Lhomond, 75231 Paris Cedex 05, France
2 Service de Physique de l'Etat Condensé, CEA Saclay, 91911, Gif-sur-Yvette Cedex, France
Accepted: 20 May 1997
We discuss a model to describe the diffuse double layer of films made with ionic soap in the presence of an additional electrolytic species. The mechanism for surface charging is explained geometrically as a consequence of the hydrophobic nature of the soap anion tails. We carry out a mean-field analysis of the system, and calculate physical observables, including the electrostatic disjoining pressure isotherm for films and the surface tension of their bulk solutions. We compare the theory with experimental results and obtain good agreement across a wide range of measurements.
PACS: 05.20.-y – Statistical mechanics / 68.10.-m – Fluid surfaces and fluid-fluid interfaces / 68.15.+e – Liquid thin films
© EDP Sciences, 1997