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.

The Ostwald ripening rate of several alkane in water emulsions stabilized by a nonionic surfactant is determined from dynamic light scattering (DLS) measurements. With the aid of computer simulations, the intensity weighted droplet radii obtained with DLS are converted to number averages, by taking the form of the droplet size distributionwhich evolves continuously toward a stationary distributioninto account. Thereby the effect of the transition from an initial, log-normal size distribution toward its stationary form is included. Second a model is proposed to account for the effect of the finite size of the surfactant layer (surrounding each oil droplet) on the measured particle size and thus on the ripening rate. It is found that both the effect of the transition from a nonstationary regime toward the stationary Lifshitz−Slyozov−Wagner regime and the effect of the finite size of the surfactant layer influence the ripening rates significantly.

The simultaneous Ostwald ripening of an emulsion and the solubilization of its oil droplets by added micellar surfactant solutions are monitored by measurements of time-averaged scattered intensities. A simple computer simulation model for the interpretation of the measurements is presented. Experimental data are analyzed with this model using one single parameter: an effective ratio of oil to surfactant molecules involved in the withdrawal of oil from the Ostwald ripening process by the added micelles. The fitted value of this parameter appears to be more than twice the one that can be predicted from the equilibrium solubilization of oil by the surfactant micelles, indicating that more oil is involved in the nonequilibrium exchange of oil and surfactant between micelles and droplets.

The evolution of the droplet size distribution of a tetradecane in water emulsion, stabilized by sodium dodecyl benzene sulfonate (SDBS) was followed by cryo-TEM during a 51 day period. As a reference for the initial distribution of a freshly prepared emulsion, the size distribution of a virtually nongrowing squalane in water emulsion was also monitored. It appears that the initial distribution is right skewed and close to log-normal with a broadness parameter of σ = 0.5. This distribution evolved rapidly to a more symmetrical one. At the end of the observation the average particle size increased by a factor of about 2.5, but the limiting left skewed distribution, predicted by the LSW (Lifshitz−Slyozov−Wagner) theory, was not obtained. The ripening rate estimated from the slope of a n 3 (a n is the number averaged radius) as a function of time is in agreement with the prediction from the LSW theory.