PHASE-EQUILIBRIA IN THE FLUORINATED SURFACTANT-ALCOHOL-WATER AND HYDROGENATED SURFACTANT-ALCOHOL-WATER SYSTEMS

To investigate the phase behavior in the ternary systems of hydrogenated and fluorinated surfactant-alcohol-water, 14 different systems of triangular phase diagrams of lithium dodecyl sulfate (LiDS)-alcohol-water and lithium perfluorooctanesulfonate (LiFOS)-alcohol-water were established for three kinds of fluorinated alcohols (CF3CH2OH, C2F5CH2OH, C3F7CH2OH) and four kinds of hydrogenated alcohols (C3H7OH, C4H9OH, C5H11OH, C6H13OH). By addition of the alcohols, the phase boundary lines of hexagonal and lamellar liquid-crystal phases in all the phase diagrams became convex to the water side; no phase separation between the hydrocarbon and fluorocarbon chains was observed and the addition of alcohol promoted the formation of these mesophases. This promotive effect increased with an increase in the carbon number of hydrogenated and fluorinated alcohols. Further, the phase stability was estimated with the limit mole fraction of alcohol/surfactant at the phase boundary. In the systems containing LiDS, the logarithms of the limit mole fraction, alco./ (alco. + surf.), for the hexagonal phase decreased linearly with the carbon number of the alcohol. In the systems containing LiFOS, the plot of the limit mole fraction for the hexagonal phase vs carbon number deviated from the line with an increase in the carbon number. These results can be correlated with the local packing model of the aggregates and the rigidity of fluorocarbon. The limit mole fraction for the lamellar phase increased stepwise with the carbon number in all the systems, which is attributed to differing loci of partitioning of the alcohol molecule in the self-associated surfactant structures. © 1992.