Modulating Aggregation in Microemulsions: The Dispersion by Competitive Intermolecular Interaction Model

A phenomenological model has been developed for the mechanism of action of phase modifiers as additives that control aggregation phenomena within water-in-oil emulsions. The “Dispersion by Competitive Intermolecular Interaction” model (DCI) explicitly considers the strength and prevalence of different intermolecular interactions that influence the molecular association of amphiphiles, the resulting distribution of aggregate size, and interaggregate interactions that influence phase phenomena. The existing “cosolvent” and “cosurfactant” association models, which describe the distribution of these amphiphiles within the solution, are re-examined in the context of intermolecular interactions. The different contributions of intermolecular interactions to the potential energy landscape of molecular association create distinct regimes within the DCI model that explain prior observations of cosolvent and cosurfactant behavior. The specific system under consideration, the N,N,N^′,N′-tetraoctyl diglycolamide amphiphile extractant with tributyl phosphate or dihexyl octanamide phase modifier additives, represents a new regime–labeled the polar disruption regime–where strong hydrogen bonding of the phase modifier with the polar-solutes disrupts the internal hydrogen bonding network of the polar micellar core, thereby decreasing aggregate size and narrowing the polydispersity in solution.