Micelle formation and aggregated state in water of sodium 1-oxo-1- [4- (tridecafluorohexyl) phenyl] -2- hexanesulfonate (FC6-HC4), a hybrid surfactant with C
6 fluorocarbon and C
4 hydrocarbon chains, were IR spectroscopically investigated.
With increasing concentration of FC6-HC4, the peak wave number for the symmetric stretching vibration of SO
3-, the hydrophilic group of the surfactant, shifted towards the higher wave number side while that for the CF
2 stretching vibration of fluorocarbon chain, one of the two hydrophobic groups, made a shift to the lower wave number side. Determination of the critical micelle concentration (cmc) of FC6-HC4, while separating the peak wave number for monomers and that for micelles, revealed that the cmc value due to the change for the hydrophilic group differs from that due to the change for fluorocarbon chain. In other words, this would suggest that the hybrid surfactant undergoes two step micelle formation, in which micelles composed of surfactant molecules with hydrated hydrophobic part (fluorocarbon and hydrocarbon chains) are formed at the first cmc and those composed of surfactant molecules with dehydrated hydrophobic part are formed at the second cmc.
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