EFFECT OF UREA ON MICELLE FORMATION OF FLUOROCARBON SURFACTANTS

The effect of urea on micelle formation of fluorocarbon surfactants was investigated by measuring conductivity cmc and fluorescence intensity of probes (1-anilinonaphthalene-8-sulfonate, auramine, and pyrene). We examined various fluorocarbon surfactants which consist of different ionic head groups, i.e., lithium perfluorononanoate (LiPFN), diethylammonium perfluorononanoate (DEAPFN), lithium perfluorooctanesulfonate (LiFOS), and 1H-1H,2H,2H-perfluorodecyl sulfate (LiHFDeS). Significant differences do exist between fluorocarbon and hydrocarbon surfactants; the cmc's of the fluorocarbons slightly decreased with the addition of urea, while those of the hydrocarbons increased as reported previously. The slight decreases in cmc's of fluorocarbon surfactants were confirmed by comparison with LiDS and LiHFDeS which contain the same ionic head group. The counterion dissociation degree of micelles always increased with the addition of urea. The micropolarities of fluorocarbon micelles were almost identical with the polarity of water, and were independent of urea concentration. The microviscosities of DEAPFN micelles decreased with urea concentration. These results suggest the significant differences in micellar characteristics between fluorocarbon and hydrocarbon surfactants.