Comparative Phase Behavior About the L2 Phase of Ternary and Quaternary Systems of Triton X-100 and Its Separated p-tert-OPEn (n = 5, 7, and 9) Components in Cyclohexane

The nonionic surfactant Triton X-100 (TX-100) is separated by preparative column chromatography into its poly(oxyethylene tert -octylphenyl ether) (OPE n ) components. The phase behavior in the neighborhood of the L 2 phase is investigated for ternary (cyclohexane/H 2 O) and quaternary (cyclohexane/H 2 O/ n -hexanol) systems of TX-100 and OPE n ( n = 5, 7 and 9). The extent of the L 2 domain and the maximum amount of water w o,max that can be solubilized by isotropic solutions strongly depend on the concentration and the length ( n ) of the polar chain of the surfactant, temperature, and the amount of n -hexanol present. Depending on these variables, with increasing w o (molar ratio of water to surfactant) some of the following phase transitions occur: L 2 → LC → L → liquid/gel → gel. Except for the liquid crystalline LC phase, all phases involved are optically isotropic, and the liquid L phase is most likely bicontinuous. Since n -hexanol is a better solvent than cyclohexane for both the surfactant and water, it destabilizes the reverse micellar and LC assemblies. Hence, its effect on the systems investigated is more prominently that of a “cosolvent” than a cosurfactant.