KINETICS OF SWELLING OF OIL-IN-WATER EMULSIONS

We have investigated the kinetics of swelling of squalane-in-water emu lsion drops by the addition of decane-in-water emulsion drops. Squalan e is sufficiently insoluble in the aqueous continuous phase that it ca nnot transfer between oil drops. Decane is able to transfer between dr ops and swells the squalane drops. The mixed emulsions were stabilized by the nonionic surfactant n-dodecyl octaoxyethylene glycol ether (C1 2E8) and were stable with respect to drop coalescence. We have made a systematic series of experiments in which the swelling rates were dete rmined as functions of the initial drop radii, volume fractions, and o il compositions of both types of emulsions. Using a theoretical model originally developed by Ugelstad et al., the entire data set was succe ssfully fitted with a single adjustable parameter equal to the product of the solubility of decane (C-infinity) and its diffusion coefficien t in the aqueous continuous phase (D). The measured value of Cinfinity D was consistent with a mechanism of decane transport in which micelle s of C12E8 act as carriers facilitating decane transport between emuls ion drops. Also in agreement with this mechanism, it was observed that increasing the aqueous phase concentration of C12E8 increased the swe lling rate. Ostwald ripening rates of the decane-in-water emulsions ga ve values of CinfinityD consistent with those derived from swelling ex periments.