Formation and charaterization of submicrometer oil-in-water (O/W) emulsions, using high-energy emulsification

Submicrometer emulsions were generated by a high-pressure wet-type jet mill and a motionless mixer called the Ramond Supermixer. Kerosene and liquid paraffin were used as the dispersed phase, aqueous sucrose and poly(ethylene glycol) solutions of PEG 400 to PEG 20000 were used as the continuous phase, and sodium dodecyl sulfate was used as a surfactant. The droplet size distribution, the Sauter mean diameter (d(32)), and the geometric standard deviation of the droplet size distribution (sigma(g)) were investigated under various combinations of the operating variables. The analysis of time-scale parameters contributed to an understanding of droplet deformation and possible re-coalescence. The relationship between the maximum droplet diameter and d(32) was determined to be a function of the ratio of the viscosity of the dispersed phase to the viscosity of the continuous phase (K). Empirical correlations were constructed for d(32) and sigma(g), and a larger similarity was determined to exist within the correlations, irrespective of the emulsifier that was used. Mechanistic models were developed to describe the droplet formation in view of droplet breakage phenomena with negligible re-coalescence. Separate models were proposed for both the turbulent inertia sub-range and the viscous subrange. For the viscous sub-range, a plot of the critical Weber number versus K revealed a rapid increase of droplet diameter at K < 0.05, regardless of the emulsifier.