Aqueous solution behavior of cationic surfactants containing sulfide linked alkyl chain

Cationic surfactants containing a thioether group in the hydrophobic chain were prepared by the reaction of alkanethiol and bromocholine bromide. The aqueous solution properties of the thio-surfactants were investigated and compared with conventional cationic surfactants. The Krafft temperatures of the thio-surfactants were lower than that of alkyltrimethylammonium bromide. The critical micelle concentrations were determined by the conductivity method, and pyrene and SPQ fluorescence probe methods. A linear relation was observed for the plots of cmc vs. chain length. However, the cmc of the thio-surfactants depended on the position of the thioether group in the hydrophobic alkyl chain. It was found that the thioether group exhibited quenching ability toward SPQ fluorescence. The variation of the surfactant monomer concentration in equilibrium with micelles can be estimated from Stern-Volmer plots.