Stability of oil-in-water macro-emulsion with anionic surfactant: Effect of electrolytes and temperature

Abstract

This paper reports on the destabilization of oil-in-water macro-emulsions prepared with diesel oil dispersed in a continuous water phase and stabilized by an anionic surfactant—sodium dodecyl benzene sulphonate (SDBS). Phase inversion temperature (PIT) of anionic surfactant–oil–water emulsion system was determined by measuring the conductivity as a function of temperature at different surfactant to oil ratios. The influence of different kinds of inorganic salts on the PIT, electrophoretic properties and long-term stability of the o/w emulsion were studied by making measurements of conductivity, zeta potential and turbidity of the emulsion. PIT was found to be a linear function of logarithmic molar concentration of the electrolytes. Droplet size distribution of stable emulsion is found to have broader range for mono-valent electrolytes than that of higher valence cations. Larger the valence of cations, lower is the stability of the emulsion. By analyzing the evolution of emulsion droplet size, and turbidity of the resulting emulsion with time, the main destabilizing mechanisms of the o/w macro-emulsion were explained. It is found that coalescence, and Ostwald ripening could be the main destabilizing mechanisms of o/w macro-emulsion.