Stability of highly charged particles: bitumen-in-water dispersions

Electric properties of crude oil/water interface play an important role in many industrial applications such as the enhanced oil recovery and road construction. The understanding of the stability mechanism of bitumen-in-water emulsions is of paramount importance in the cold technology of road construction. The stability (or instability) of the emulsion directly affects the transport, the storage and the application on rocks of bitumen emulsions, whereas it has an indirect influence in the final adhesion bitumen–rock. The high values of electrophoretic mobility found for bitumen particles at high pH as well as the charge inversion at low pH are explained by the presence of ionizable surface groups on the bitumen surface. The elevated surface charge density of the spherical bitumen particles brings about that they can be considered as a model system for verifying the electrophoretic relaxation effect experimentally as well as studying the validity of certain standard electrokinetic theories for spherical colloidal particles. Accordingly, the zeta potential was calculated by using different methods such as the classical models (Booth and Overbeek), the exact computation (OʹBrien and White) and recent theories (Ohshima). The Hamaker constant of bitumen in water was computed by means of the Lifshitz theory and the simple spectral method from the dielectric responses of alkanes. The stability results suggest that the bitumen dispersion does conform the DLVO theory. In contrast, Non-DLVO forces (such as the “hydrophobic” force) were not observed in this system.