Bitumen-in-water emulsions stabilized with natural surfactants

The stability and rheological properties of bitumen-in-water emulsions prepared in the presence of different concentrations of sodium carbonate in the aqueous phase were investigated. When the carboxylic acids present in the bitumen are contacted by an alkaline aqueous solution, surface-active compounds or natural surfactants are formed. These surfactants are responsible for the very low values of interfacial tensions observed and for the stabilization of the bitumen-in-water emulsions formed. The mean droplet diameter of the emulsions prepared decreased as the concentration of sodium carbonate increased. The apparent viscosity of the emulsions also increased with the sodium carbonate concentration. Eventually, a sodium carbonate concentration was reached at which emulsions were completely unstable. Results are explained by considering that, at low electrolyte concentrations, emulsions are stabilized by electrostatic repulsion forces between the electrical double layers, while at high electrolyte concentrations, the short-range interaction forces are predominant. (C) 2001 Academic Press.