Polyelectrolyte-surfactant interaction and its influence on flocculation and coalescence of oil-in-water emulsions

The strong interactions between the cationic polyelectrolyte and the anionic surfactant sodium dodecyl sulfate were characterized by means of precipitation and redissolution study in aqueous solutions. The main driving force for the association complexation between two components is the electrostatic charge neutralization. By using silicone oil-in-water emulsions as a model system, we present the factors that influence the stabilization and destabilization of the emulsions: surfactant concentration, flocculant concentration, oil droplet size, interfacial tension and zeta potential. Cationic polyelectrolytes were used as a flocculant to destabilize the emulsion by reacting with the anionic surfactant sodium dodecyl sulfate to form an insoluble complex. The optimum flocculation concentration of cationic polymer required for neutralizing the negative charges of surfactant increases proportionally to the concentration of surfactant but inversely proportionally to the charge density of polymer. Flocculation and coalescence of emulsions with a dual polymer combination of moderate and low cationic charge densities with an intermittent dosing method is compared with a single polymer system. Analysis of the turbidity removal and coalescence results under corresponding conditions showed that the dual polymer system produces an appreciably better destabilization of emulsions through a synergistic combination of electrostatic charge neutralization and polymer bridging mechanisms.