EFFECTS OF COSURFACTANT AND OIL CHAIN-LENGTH ON PHASE-BEHAVIOR AND SOLUBILIZATION IN ALCOHOL AND GLYCOL ETHER MICROEMULSIONS

The phase behavior and oil solubilization capacities of a series of model microemulsion systems have been studied. Phase behavior was studied in systems composed of NaCl brine, sodium dodecyl sulfate, and either 1-butanol, 1-pentanol, ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, ethylene glycol monohexyl ether, or diethylene glycol monohexyl ether. It was found that longer chained cosurfactant systems exhibit isotropic behavior over smaller compositional ranges. Whereas the ethylene glycol monohexyl ether system was found to possess two separate isotropic microemulsion-type regions, all other systems were found to possess connected isotropic regions. The one-phase regions in the 1-pentanol system, however, are connected by a narrow channel. Finally, it was determined that increasing the degree of amphiphilicity in the cosurfactant tends to increase the occurrence of liquid crystal phases. The effects of changing the cosurfactant structure and the oil chain length on oil solubilization were also analyzed. We introduce the method of presenting solubilization data in the form of contour plots, and demonstrate the utility of these plots for understanding solubilization. It was generally found in both alcohol and glycol ether systems that lengthening the cosurfactant chain or shortening the oil chain tended to increase solubilization and drive the systems to be more dependent on the amount of cosurfactant and less on the amount of surfactant. In the ethylene glycol monohexyl ether system, it was found that liquid crystals could be formed when octane or dodecane was solubilized and high concentrations of amphiphiles were present, but not when hexadecane was solubilized. The trends in solubilization were able be to be qualitatively described by Winsor's R ratio analysis which may provide a means of performing direct calculations to predict behavior in these systems.