Effect of Addition and Molecular Size of Triglyceride Oils on Phase Behavior and Surfactant Self-Assemblies

The cloud temperature of C12EO8 aqueous solution decreases by solubilizing triglyceride oils (1,2,3-trihexanoylglycerol (THG), 1,2,3-trioctanoylglycerol (TOG) and 1,2,3-tridecanoylglycerol (TDG)). The reduction of cloud temperature is larger with the oil having shorter alkyl chains. In the water/C12EO8 system, a micellar, a hexagonal, a bicontinuous cubic and a lamellar phases are successively formed with increasing surfactant concentration at 25°C. A discontinuous cubic phase is formed by adding TOG to the aqueous C12EO8 system. SAXS measurement was performed on the discontinuous cubic, hexagonal and lamellar phases and molecular parameters such as effective cross sectional area per surfactant molecule, radius of micelle for the discontinuous cubic and the hexagonal phases, half-thickness of bilayer of the lamellar phase were obtained. The changes in the molecular parameters by increasing TOG content suggest that most of the oil molecules are solubilized in the core of surfactant aggregates. Thermal stability of the discontinuous cubic phase increases. The amount of solubilized oil in the discontinuous cubic phase increases by increasing temperature and decreasing oil molecular weight.