Local Interfacial Migration of Clay Particles within an Oil Droplet in an Aqueous Environment

Abstract

We discuss the interfacial migration due to Marangoni forces of clay particles within an oil droplet that is immersed in water, which is relevant for the formation kinetics of Pickering emulsions. Hydrophilic (MMT) and hydrophobic (OMT) clays are studied, where the hydrophilic clay particles adsorb in the oilwater interface, contrary to the hydrophobic clays. The feasibility of an imagetime correlation technique is discussed, in order to probe the local interfacial migration velocities of clay particles in the oil droplet. Here, correlation functions are constructed from time-resolved images, in order to quantify the local migration of clay particles. Correlation functions are measured at different waiting times, that is, the time after formation of the droplet. The initial decay rate and the baseline of these correlation functions depend on the waiting time in a qualitatively different way for the two clays, which is attributed to the different interfacial migration behavior for the hydrophilic, adsorbing clays and the nonadsorbing, hydrophobic clays as a result of the Marangoni effect.