Molecular thermodynamic modeling of droplet-type microemulsions.

Microemulsions are nanoheterogeneous, thermodynamically stable, spontaneously forming mixtures of oil and water by means of surfactants, with or without cosurfactants. The pledge to use small volumes of amphiphile molecules compared to large amounts of bulk phase modifiers in a variety of chemical and industrial processes, from enhanced oil recovery to biotechnology, fosters continuous investigation and an improved understanding of these systems. In this work, we develop a molecular thermodynamic theory for droplet-type microemulsions, both water-in-oil and oil-in-water, and provide the theoretical formulation for three-component microemulsions. Our thermodynamic model, which is based on a direct minimization of the Gibbs free energy of the total system, predicts the structural and compositional features of microemulsions. The predictions are compared with experimental data for droplet size in water-alkane-didodecyl dimethylammonium bromide systems.