Ostwald ripening in macro- and nanoemulsions

Characteristic features of the Ostwald ripening in oil-in-water and water-in-oil macro- and nanoemulsions are analyzed. Methods for reducing the ripening rate are considered. It is shown that Ostwald ripening is especially relevant for nanoemulsions, and this is often the main process leading to degradation of nanoemulsions, thus limiting their practical applications. Considerable attention is paid to the debatable issue of the role of surfactants in the mass transfer between the droplets of the dispersed phase. Analysis of published sources shows that if the solubility of the dispersed phase substance in the dispersion medium is not extremely low, then the major contribution to Ostwald ripening is made by molecular diffusion. If the solubility of the dispersed phase substance is very low, then micelles and nanodroplets are the most likely carriers of the substances through the dispersion medium. Nanodroplets and slightly larger droplets are formed on the surface of droplets of the starting emulsion because of the interfacial instability (Marangoni effect).
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