Effect of hydrophobic tail on the mixed micelles of diheptanoylphosphatidycholine with cationic and zwitterionic surfactants: a fluorescence study

The pyrere fluorescence measurements have been performed for the mixtures of diheptanoylphosphatidycholine (DHPC) with dimeric cationic, phosphonium cationic, and zwitterionic surfactants of C10 to C16 hydrocarbon tail length over the whole mixing range. From the I1/I3 versus total surfactant concentration plots, the mixed critical micelle concentration (cmc) of various mixtures was computed. The nature of the mixed micelles between the unlike components was determined by applying the regular solution theory. It was observed that all the mixtures show attractive interactions between the binary components and the interactions becomes more intense with the increase in length of the hydrocarbon tail of cosurfactant. The increase in the length of cosurfactant allowed greater amount of DHPC to be accommodated in the mixed micelles, which in return brought stronger synergism. A variation in the Stern-Volmer constant, KSV, further supports these results.