An investigation into the relationship between catastrophic inversion and emulsion phase behaviors

The catastrophic inversion process from an oil-continuous to a polar phase-continuous emulsion was investigated with a system consisting of silicone oil, water and a nonionic surfactant. The polar phase involved an aqueous micellar solution, an inverse micellar solution, a hexagonal liquid crystal and a lamellar liquid crystal. Results indicated that a suitable polar phase structure with a positive spontaneous curvature was required for the formation of multiple emulsions leading to inversion at a relatively low dispersed phase fraction. Differences observed in the inversion pattern and the resultant drop size were explained in terms of the rheology of the polar phase and interfacial tension. The inverted emulsions were gel emulsions exhibiting similar viscoelastic behavior regardless of the specific polar phase structure. The same viscoelastic behavior was also exhibited in a lamellar liquid crystal (but not in a hexagonal liquid crystal) suggesting a common response mechanism to shear.