Study of the electrical properties of cationic bitumen emulsions by microelectrophoresis

Abstract

We investigate in the present work, the effects of the emulsifier nature and content on the aqueous phase viscosity and on the zeta potential of cationic bitumen emulsions, in the pH range 2–13. The bitumen in water emulsions was prepared at pH values in the range 2–2.4 and in the presence of complementary emulsifiers’ pair made of protonated amine 70 wt.% and a quaternary ammonium salt 30 wt.%. The final bitumen and emulsifier content in the emulsion were, respectively, 60 vol.% and 0.4–1.0 wt.%. For emulsions having emulsifier content in the range 0.4–0.7 wt.%, the magnitude of the zeta potential decreases as the pH increases and reaches a plateau value at pH 10, which corresponds to the pKa of the protonated amine. In the same pH range 2–13, the aqueous phase viscosity remains constant up to pH of approximately 10, increases slightly thereafter and levels out. However, for emulsions having 1 wt.% emulsifier content, the magnitude of the zeta potential decreases as the pH increases, reaches a minimum value at pH of approximately 11, and increases up to pH of approximately 13. For these systems the aqueous phase viscosity–pH curve remains constant up to pH of approximately 9, shows a pick having maximum at pH 11, and decreases thereafter. Thus, evidence of synergistic effects is observed when the protonated amine surfactant loses its functionality at pH values approximately 10, leading to high the aqueous phase viscosity and low surface electrical charge of the bitumen droplet. Further, the pH values at which the weakly flocculated bitumen emulsions are obtained coincide with the pH at which high aqueous phase viscosities and low droplet electrical surface charges are observed. This study shows that by adjusting the nature and the composition of the emulsifiers, we can control both the rheology and the surface electrical charge of bitumen emulsions. The rheology and the electrical properties determine in turn the stability of the system.