Influence of non-ionic surfactants on the equilibrium distance of approach of emulsion droplets

Abstract

The equilibrium distances between two n-octane droplets in aqueous solutions of non-ionic sucrose surfactants were measured as a function of surfactant and of added electrolyte concentration. From the equilibrium film thickness, values of the Hamaker coefficient and the surface potential were calculated. Increasing the electrolyte concentration at constant surfactant concentration reduced the film thickness. Increasing the surfactant concentration at constant electrolyte concentration increased the film thickness. The results were analysed in terms of a simple three-layer oil–water–oil model, which showed that increasing the concentration of surfactant increased the repulsive forces.

The rate of thinning of the films was determined and used to calculate the disjoining pressure as a function of the distance between the oil droplets as they approached.