Ostwald Ripening of Alkane Emulsions in the Presence of Surfactant Micelles

Abstract

The effect of sodium dodecyl benzenesulfonate (SDBS) surfactant micelles on the Ostwald ripening was investigated by several experiments and by computer simulation. The experimental ripening rates determined by dynamic light scattering were about 2 times higher than the one predicted by the Lifshitz−Slyozov−Wagner (LSW) theory. This increase is attributed to an increase of the concentration of oil molecules in the continuous phase. The increase in solubility and hence in ripening rates is predicted by Kelvin's equation, assuming the presence of small oil droplets of the size of the micelles. A study of the solubilization kinetics of emulsion oil droplets into micellar solutions confirms that the main rate-determining mechanism for the exchange of oil between droplets and micelles is molecular diffusion through the continuous phase. Finally the combination of the simulation of Ostwald ripening in the presence of an oil sink with the experimental monitoring of the ripening of emulsions to which continuously a micellar solution is added, confirms the previous model for the transport of oil. There is also evidence that the surfactant micelles are not in local equilibrium with the oil molecules.