The Adsorption of Dodecyldimethylammonium Bromide on Aqueous Surfaces of Sodium Bromide Solutions

Abstract

Abstract The surface tension of aqueous NaBr solutions of dodecyldimethylammonium bromide has been measured by the drop weight method at different surfactant and NaBr concentrations. By applying the Gibbs adsorption isotherm, surface excess densities of surfactant cation, Na+ and Br− are derived as functions of surfactant concentration at different NaBr concentrations. The rational mean activity coefficients of surfactant and NaBr are both approximated by a common expression satisfying the Brφnsted principle for mixed electrolytes and containing the ionic strength as a variable. Surface excess density of surfactant cation increases with increasing surfactant concentration and has a general tendency still increasing even at the critical micelle concentration. Some comparison of the behavior of surface excess densities of ions between the present bromide system and the previous chloride system is made. The Corrin-Harkins plot for the critical micelle concentration consists of two straight lines intersecting at 0.015 mol dm−3 NaBr.