INTERFACIAL MICROPOLARITY IN THE MICELLAR REGION OF THE SODIUM (2-ETHYLHEXYL) SULFOSUCCINATE (AOT) INVERTED MICELLES

The fluorescence lifetime (τF) of 2-(p-dimethylaminophenyl)-3,3-dimethyl-3H-indole (1) in various AOT aqueous micellar solutions is reported in methylcyclohexane and n-heptane. It is shown that the probe resides at the interfacial region of the inverted AOT micelle. The variation of τF-1 with the molar fraction of water follows a single experimental exponential law which is similar to the one observed in p-dioxane/water mixtures. This shows that no dielectric enrichment of the probe is taking place in the reversed micellar solution and that the "solvation" of the probe in AOT is similar to that in p-dioxane. This allows one to obtain dielectric constants at the micellar interface using the fluorescence lifetime in p-dioxane/water mixtures as a polarity ruler. Moreover it was shown that the dielectric constant increases linearly with the mole fraction of water. © 1990.