Breaking of a cationic amine oil-in-water emulsion by pH increasing: Rheological monitoring to modelize asphalt emulsion rupture

Abstract

When a caustic soda solution is slowly added up to a cationic oil-in-water emulsion, prepared with dodecylamine as surfactant, the chemical equilibrium is altered. As a consequence, a progressive viscosity diminution is observed until complete emulsion destabilization. Original cationic emulsions are stable thanks to the droplet electrical double layer formed by the ionized surfactant adsorption on the liquid interface at very low pH values. However, the alkali addition changes the chemical equilibrium in different ways, such as reducing the hydronium ion concentration, allowing for dodecylamine deionization and increasing the ionic species concentration. These changes and the fact that the emulsion's droplet size and distribution remain constant (noticed by granulometric measurements) during the process, let us assuming that viscosity decreases as a consequence of the overall positive layer charge diminution. However, emulsion destabilization can be explained in terms of some formulation parameters such like SAD or HLD. Our system evolves from a very negative to a positive HLD value passing through the optimal formulation when destabilization is observed. An interfacial formulation analysis is presented and a hypothetically extrapolation to asphalt emulsions is briefly analyzed.