Water Transport by Nanodispersion Droplets in a Water-in-Oil Emulsion

Abstract

The mechanisms of water transport through an organic dispersion medium are considered for an emulsion during Ostwald ripening and for a three-phase system upon a contact of a water-in-oil emulsion with an external aqueous phase. Electron microscopy shows a formation of nanodispersion droplets during the diffusion of water through the organic phase of water-in-oil emulsions. The experimental water diffusion coefficient during Ostwald ripening in emulsions is 40 times smaller than the calculated molecular diffusion coefficient. The experimental diffusion coefficients are determined for rhodamine C, which solubilizes in the surfactant micelles, and for ethyl alcohol, a cosurfactant, which reduces the interfacial tension in the emulsion and promotes the formation of nanodispersion droplets. The experimental diffusion coefficients of rhodamine C and ethanol are three orders of magnitude smaller than the calculated values. The ratio between the numbers of rhodamine C and water molecules diffusing through the organic phase is 1 : 10 000. The nanodispersion droplets are shown to make the main contribution to the water transport in the organic dispersion medium of the emulsions. Water can also be transported by single surfactant molecules, but this mechanism is not the predominant one.