Ostwald ripening in emulsions

Abstract

Ostwald ripening in emulsions is reviewed, with particular emphasis on the application of the Lifshitz, Slezov and Wagner theory to emulsion systems. The rate of ripening within single component disperse phase emulsions can be described using this theory, provided certain parameters are known, these being the solubility and diffusion coefficient of the disperse phase within the bulk phase, the interfacial tension between the droplets and the bulk phase. The rates of ripening (defined as the rate of change in the cube of the average radius with time) are shown to be linearly dependent upon the interfacial tension below the CMC of the surfactant stabilizing the emulsion, but show only a weak dependence upon the concentration of micelles above the CMC. The effects of the addition of a less soluble component to the disperse phase is also discussed in terms of the treatment given by Kabal'nov et al. It is found that the addition of a longer chain homologue to the disperse phase significantly retards the rate of ripening. This is in accordance to that predicted by the treatment of Kabal'nov et al. The implications that these results have on alkane solubility in water are also discussed and it is concluded that the solubilities of alkanes decrease in water with increasing chain length up to at least octadecane, a result contrary to that reported in the literature.