Aggregation of novel betaine surfactants N-(3-alkoxy-2-hydroxypropyl)-N, N-dimethylglycine in aqueous solution : Micellization and microenvironment characteristics

In aqueous solution aggregation behaviors and the microenvironment characteristics of the micelle assemblies of five novel betaine surfactants, N-(3-alkoxy-2-hydroxypropyl)-N,N-dimethylglycines, have been investigated by steady-state fluorescence and time-resolved fluorescence decay techniques using pyrene and 1,6-diphenyl-1,3,5-hexatriene as fluorescence probes. Critical micelle concentrations (cmc's), mean micelle aggregation numbers, micropolarities, and microviscosities of these surfactant micelles in the absence and presence ofinorganic salt have been determined. Logarithmic cmc, logarithmic aggregation number, and logarithmic microviscosity of these surfactant micelles increase linearly with alkyl chain length but are moderately dependent on the concentration of added salt. The micropolarity of these surfactant micelles is also moderately dependent on salinity; however, contrary to cmc, aggregation number, and microviscosity, it is independent of the alkyl chain length. The microviscosity of these micelles is found to be severalfold higher than ionic micelles but is lower than that of nonionic micelles. These results suggest that those betaine zwitterionic surfactants are intermediate between ionic and nonionic surfactants in terms of aggregation behavior, micelle micropolarity, and micelle microviscosity.