Phase equilibria and microemulsion structure for a triple-chained soap: Sodium di-2-butyldecanoate

Abstract

An alkyl carboxylate with a very voluminous hydrophobic part, sodium di-2-butyldecanoate, was prepared and its phase behavior investigated in mixtures with water (25–100°C) and in mixtures with both water and decane (25°C). Furthermore, the homogeneous phases formed were characterized on the basis of NMR and self-diffusion studies. In the two-component water-surfactant system there is an extensive lamellar liquid crystalline phase region as well as two isotropic solution regions, one at lower and one at higher surfactant concentrations than the lamellar liquid crystalline region. The latter solution phase has unusual features in respect to location in the phase diagram, solution structure, and the formation of metastable lamellar phase, transforming slowly into isotropic solution. Sodium di-2-butyldecanoate can mix equal amounts of water and hydrocarbon into homogeneous solution and the water-to-hydrocarbon ratio of the microemulsions can be varied over very large ranges. Depending on composition, the microemulsion microstructure is of the water droplet-in-oil type or bicontinuous.