Spectroscopic studies on the microemulsions and lamellar phases of the system triton X-100:hexanol:water in cyclohexane

Abstract

The system Triton X-100-hexanol-cyclohexane-water is studied by spectroscopic methods. Results pertaining to NMR, fluorescence maxima and quantum yields of 8-anilinonaphthalene-sulfonic acid (ANSA), the solvent-sensitive n → π^∗ transition of solubilized nitrate ion, and pH measurements by solubilized indicators are presented. The NMR results show that initial addition of water to a dry 20% w/v solution of the surfactant mixture in cyclohexane leads to the formation of reverse micelles with a decrease in the mobility of the ethylene oxide chains. At low concentrations, most of the water is bound to the ethylene oxide groups, but at higher water concentrations more and more water is present in its free form in water pools. When the Triton X-100: hexanol ratio is 4:1, a liquid crystalline phase is formed at water concentrations above 9%. NMR results show that in this phase, both water and the ethylene oxide chains have low mobility. Results from ANSA fluorescence are interpreted in the light of the NMR results. Dye indicator absorbance measurements show that in this system, water in the water pools is not significantly different from bulk water in its features.