Comparative phase behavior about the L-2 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) (OPEn) components. The phase behavior in the neighborhood of the L-2 phase is investigated for ternary (cyclohexane/H2O) and quaternary (cyclohexane/H2O/n-hexanol) systems of TX-100 and OPE, (n = 5, 7 and 9). The extent of the L-2 domain and the maximum amount of water omega(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 omega(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.