Interfacial film of surfactant adsorbed at a solid/liquid interface

Abstract

Based on the two-step adsorption model, the isotherm equations for individual adsorptions of surfactant monomers and hemi-micelles and for the unoccupied sites at a solid/liquid interface have been derived. In this way the compositions of the adsorption films were determined. By combining the general isotherm equation for adsorption of surfactant at a solid/liquid interface (B-Y. Zhu and T. Gu, J. Chem. Soc., Faraday Trans. 1, 1989, 85, 3813) with the Gibbs adsorption equation, solid/solution interfacial pressures at various concentrations may be calculated. The π–C and π–A curves for real systems have been provided. It is revealed that there are different states, including a liquid expanded film, a liquid condensed film and a transitional phase, in the interfacial film of surfactant adsorbed on a solid.