Solubilization of Hydrocarbon Emulsion Droplets Suspended in Nonionic Surfactant Micelle Solutions

Abstract

The mass transport of nonpolar molecules from emulsion droplets to surfactant micelles was studied using a static light scattering technique. A series of n-hexadecane oil-in-water emulsions were prepared with varying droplet concentrations (0−0.05 wt %) and mean droplet diameters (0.17−0.73 μm). Emulsion droplets were suspended in either pure water or water containing nonionic surfactant micelles (2 wt % polyoxyethylenesorbitan monolaurate). The time dependence of the droplet concentration and size distribution were monitored using light scattering. In the absence of surfactant micelles the size and concentration of oil droplets remained constant, but in their presence the droplet concentration decreased with time and the mean droplet diameter increased. The kinetics of the solubilization process depended strongly on the initial droplet size and concentration. Our experimental observations can be explained in terms of two opposing physical mechanisms: solubilization (which tends to decrease the mean droplet size) and Ostwald ripening (which tends to increase the mean droplet size).