Abstract
The mixed surfactant solutions of lithium perfluoro-octane sulfonate(LiFOS)-lithium dodecyl sulfate(LiDS), LiFOS-hexaethyleneglycol dodecylether (6ED), and LiFOS-lithium perfluorooctanoate(LiPFO) have been investigated by means of surface tension and pyrene fluorescence probing. The miscibility in these systems increases in the order: 6ED-LiFOS 〉 LiFOS-LiPFO 〉 LiDS-LiFOS. Measurements of the pyrene fluorescence lifetime and the ratio I1/ I3 of the intensities of the first and third bands of the pyrene monomer fluorescence spectrum appear to indicate that only one type of mixed micelle exists in the mixed systems of LiDS-LiFOS and 6ED-LiFOS. The effect of hydrocarbon (methanol to hexanol) and fluorocarbon (fluoroethanol to fluoropentanol) alcohols on the mixed surfactant systems has also been investigated. From the rate of CMC change with the added alcohol concentration, it has been demonstrated that micelle formation of LiFOS is less affected by a lowering of the dielectric constant compared with LiDS and that the effects on the CMC depression is larger for the surfactant-alcohol pair which has the same kind of alkyl chain. Further, in a single surfactant system, the rate of CMC change with alcohol is related linearly to the partition coefficient evaluated by measuring the vapor pressure of alcohol. In all the mixed systems, the change in the partition coefficient of alcohol against the mixed micelle composition is similar to that of mixed CMCs.
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