Location of solubilized oil in lyotropic surfactant liquid crystalline phases and the resulting effects on phase equilibria

Abstract

The location of solubilized oil in surfactant liauid crystalline aaareaates can have a pronounced effect on phase stability and their compositional extent. -Detaiied experimentd ternary phase diagrams of sodium 1-tetradecanoate, water, and four different hydrocarbons-n-decane, n-hexadecane, toluene, and 1decanol-are presented. The phase diagrams were constructed through two primary methods: optical birefringence and quadrupole NMR spectroscopy. The results reveal a strong dependence of liquid crystalline phase stability on oil type, through the location of solubilized oil in the surfactant aggregate. n-Decane and n-hexadecane are shown to be primarily solubilized in the interior or core of the aggregates, toluene is solubilized in both the core and palisade or interfacial layer, and 1-decanol is primarily solubilized in the palisade layer. A simple geometric model of core and palisade solubilization is able to rationalize the shape of the ternary liquid crystalline single phase regions comprised of cylindrical hexagonal phase aggregates. Quadrupole NMR spectroscopy of deuterated toluene confirms ita solubilization in both core and palisade regions in lamellar phases.