CAN MICELLES MEDIATE A MASS-TRANSFER BETWEEN OIL DROPLETS

The effect of sodium dodecyl sulfate concentration on the rate of Ostwald ripening in undecane-in-water emulsions was studied. Varying the surfactant concentration from 0.03 to 1 M virtually did not affect the Ostwald ripening rate, despite a considerable increase in solubilization. The observed rates were close to the estimate based only on the molecular solubility. To explain this behavior, it was argued that (i) SDS micelles cannot absorb the oil directly from the emulsion droplets and the stage of a molecular diffusion through the medium is a necessary step and (ii) the micelles are not in a local equilibrium with the oil-in-water molecular solution, presumably because the rate of the oil monomer exchange between the aqueous solution and the micellar interior is quite low.