Influence of molecular structure of hydrocarbon emulsion droplets on their solubilization in nonionic surfactant micelles

Light scattering was used to study the mass transport of hydrocarbon molecules from emulsion droplets to nonionic surfactant micelles. The hydrocarbons used as the dispersed phase of the emulsions were: 1-tetradecene, n-tetradecane, 1-hexadecene, n-hexadecane, 1-octadecene and n-octadecane. Oil-in-water emulsions were prepared which had the same initial droplet diameter (0.3 μm), but different droplet concentrations (0 to 0.05 wt.%). The emulsion droplets were then suspended in either pure water or an aqueous micellar nonionic surfactant solution (2 wt.% polyoxyethylene sorbitan monolaurate) and the time-dependence of the droplet concentration and size distribution monitored at 30 °C using static light scattering. In the absence of surfactant micelles the size and concentration of the hydrocarbon droplets remained constant, but in their presence the droplet concentration decreased with time, and the mean droplet diameter increased, indicating that solubilization occurred. The growth in droplet size with time is attributed to enhanced Ostwald ripening in the presence of surfactant micelles. The mass-transport rate of oil molecules from droplets to micelles, the growth in droplet size with time and the maximum amount of oil solubilized per unit amount of surfactant, increased in the following order: n-octadecane<1-octadecene<n-hexadecane<1-hexadecene< n-tetradecane<1-tetradecene.