Intertwining Roles of the Disperse Phase Properties during Emulsification.

Abstract

The combined effect of viscosity ratio, interfacial tension, and disperse phase density on the process of droplet formation during emulsification was evaluated. For that aim, emulsification by ultrasonication of oil/water systems with viscosity ratios between 1 and 600, with and without surfactant was performed. The time evolution of the average droplet size was estimated by dynamic light scattering measurements. For viscosity ratios between 1 and 200 in the presence of surfactant, our results partly reproduce those of the intriguing U-type reported in the literature. Beyond that range, the droplet size decreases, as the viscosity ratio rises. For surfactant-free systems, the size is slightly affected by the increase in viscosity. This complex scenario is analyzed in terms of both the individual and intertwined roles of interfacial tension, viscosity, and density ratios: (1) if the interfacial tension dominates, the droplet rupturing process is independent of its internal properties, and inversely, (2) if the interfacial tension is low, the internal properties play a major role in the rupturing of the droplet. Finally, we identified a scenario in which the retarded addition of surfactant leads to emulsions with a stability similar to those with the surfactant added at the beginning, saving energy and time.