Evaluation of Heat of Bilayer Formation by Surfactant in Thin Liquid Film

Abstract

In the foam film stabilized by surfactant, a bilayer film of the surfactant is formed at the surfaces. For such a thin liquid film, thermodynamic relational expressions dealing with the thermodynamic quantity changes with the formation of bilayer film can be derived by introducing the divided planes on both surfaces of the thin film to define the interfacial excess quantities. By applying the obtained thermodynamic relations to the temperature dependence of film tension, it is possible to estimate the enthalpy change corresponding to the heat of bilayer film formation. The analysis for the black foam film of the aqueous tetradecyltrimethyammonium bromid and NaBr solution was conducted and then it was demonstrated that the heat of bilayer film formation reflects a minute change of the counter ion condensation in the bilayer of Newton black film.