1-METHYL-8-OXYQUINOLINIUM BETAINE MOIETY AS A PROBE OF SURFACTANT SELF-ASSEMBLY SYSTEMS

The factors that influence the solvatochromism and acid-base behaviour of 5-octadecyl-1-methyl-8-oxyquinolinium betaine (FOEHQ) and 7-octadecyl-1-methyl-8-oxyquinolinium betaine (SOEHQ) in aqueous micellar systems have been identified. This has been achieved by comparing the spectral and acid-base properties of FOEHQ and SOEHQ in the surfactant self-assembly systems with those of FOEHQ and SOEHQ in 1,4-dioxane/water mixtures and those of 1-methyl-8-oxyquinolinium betaine (MEHQ) in both 1,4-dioxane/water mixtures and aqueous electrolyte solution. It is concluded that the solvatochromism of the MEHQ moiety can be employed to obtain information about the interfacial solvent properties of surfactant/water interfaces. The acid-base equilibrium of the MEHQ moiety can be influenced by the presence of anionic solution species. The effect that this can have on the utilization of FOEHQ and SOEHQ as probes of the electrostatic characteristics of surfactant/water interfaces is discussed.