Emulsions provide a means to deliver mutually immiscible liquids in a macroscopically uniform manner. Multiple-phase emulsions in particular provide a useful template for fabrication of composite materials. The challenge in synthesizing multiple-phase emulsions or composites lies in the ability to design and control the morphology of the multiple-phase system in order to arrive at the desired properties. Multiple emulsions with sophisticated and precisely controlled structures have been well demonstrated via microfluidic techniques that generate one droplet at a time from a capillary. Large scale industrial production of emulsions, on the other hand, relies on the rapid mixing of large quantity of fluids at scales of metric tons instead of grams. Being able to predict and control multiple-phase emulsion structure in this latter case is therefore commercially pivotal. The morphology in a multiple-phase emulsion is governed by equilibrium tensions and volume fractions in accordance with thermodynamic principles. This has been well demonstrated in academic studies but under-appreciated in the formulation world. Equilibrium properties tend to escape the formulator’s mind, as emulsions, after all, are kinetically stabilized systems. This talk brings attention to two types of 3-phase emulsions to demonstrate practical value of (thinking) thermodynamics as well as to illustrate additional insights previously not recognized. The first type of 3-phase emulsion is formed from aqueous suspension polymerization of a solution mixture of silicone and acrylate monomers, which upon polymerization phase separates into two phases within each emulsion droplet. The morphology as well as detailed geometry of the hybrid particle are uniquely defined by the composition of the formulation. The second type of 3-phase emulsion is formed from mechanical dispersion of two immiscible oils in water. In this latter case the morphology of the hybrid droplet is defined by the equilibrium tensions, but specific geometry varies from droplet to droplet owing to random volume combination during the disruptive dispersion process. In both cases, predicted emulsion structure based on equilibrium properties is shown to agree with experimental observations.

Thermodynamics: The invisible arbiter of emulsion structure; insight from an examination of three-phase emulsions

ACS Spring Meeting 2021

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