The invisible arbiter of emulsion structure: insight from an examination of two types of 3-phase emulsions

Abstract

It has long been established that the equilibrium properties of a water–oil–surfactant system governs the morphology of the emulsion formed—an inherently non-equilibrium system. In this work, we reinforce this concept and bring forward additional insights. Two types of 3-phase emulsions are examined, one obtained from suspension polymerization of silicone and acrylate in an aqueous phase and another obtained from mechanical dispersion of a silicone oil and a sunflower seed oil into an aqueous phase. We show that the specific emulsification process has an impact on the detailed structure of the final multiple droplets. In suspension polymerization, the complete miscibility of silicone with acrylate monomers prior to polymerization renders uniformity in the composition of the starting droplets; hence the final droplets after polymerization all have identical equilibrium tensions as well as relative volume ratios between the separated phases. Consequently, the final droplets have uniformly the same structure as predicted based on thermodynamics. On the other hand, the 3-phase emulsion formed from mechanical dispersion of two immiscible oils in water shows an overall morphology that is predicted by equilibrium tensions, however, a wide variation in the specific geometry is observed. This latter aspect reflects the randomness in drop break-up-and-recombination associated with the homogenization process, which results in variable volume ratio between the two immiscible oils among different droplets.