Deconvoluting Emulsion Stabilization Mechanisms Using Diffusing Wave Spectroscopy

Traditional methods to study emulsions are unable to provide mechanistic descriptions of the modes of action of emulsifier and stabilizer additives. We develop diffusing wave spectroscopy (DWS) to study water-in-oil emulsions and three different commercial emulsion stabilizers. By tracking the time evolution of the transport mean free path, l*, and an anomalous diffusion parameter, a, we show that DWS measurements can provide insights into physical dynamics that are inaccessible through conventional techniques. Using DWS, we can determine a specific mechanism of action for each stabilizer. The first two stabilizers are both effective emulsifiers and act primarily at the drop interface. The surface activity increases the friction factor and hinders the droplet motion. The third is a less effective emulsifier but rather acts to modify bulk phase viscosity and reduce the frequency of droplet interactions. We anticipate that DWS can be used to provide mechanistic insights into emulsion formulation development.