On the Determination of Ostwald Ripening Rates from Dynamic Light Scattering Measurements

Abstract

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 distributionwhich evolves continuously toward a stationary distributioninto 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.