Effect of the organic solvent on the interfacial micropolarity of AOT-water reverse micelles

摘要

A study has been made on the effect of the organic solvent upon the properties of the interface of reverse micelles formed by sodium his (2-ethylhexyl) sulfosuccinate (AOT) - water. The study has been performed using fluorescence and absorption spectroscopies. The probes considered were 8-anilinonaphtha lene-l-sulfonate (ANS(-)) and ruthenium tris[(bipyridine)](2+), [Ru (bpy)(3)](2+), in fluorescence spectroscopy, and E-T (30) in absorption spectroscopy. These probes were selected since its spectroscopic behaviour depends on the micro polarity of the medium. Furthermore, they have equal charge (ANS(-)), opposite charge [Ru(bpy)3](2+) than that of the micelle, or its nature is zwitterionic (E-T (30)), which allows for the sensing of the interfacial properties at different depths. The study has been performed at different W = [water]/[AOT] values ranging from ca. 1-2 up to saturation in the external solvent considered. Organic solvents employed were: n-heptane, n-hexane, isooctane, dodecane cyclohexane, benzene, toluene, cumene, chlorobenzene, dichlormethane (DCM), 1,2-dicholoroethane (1,2-DCE) and tetrachloroethylene (TCE), and the results are discussed taking n-heptane as reference solvent. For the three probes considered, n-hexane, isooctane, dodecane and cyclohexane behaves similarly to n-heptane over all the range of W values considered, irrespective of the probe employed. ANS(-) behaviour in benzene, toluene and TCE is similar to that observed in aliphatic hydrocarbons. Cumene, chlorobenzenc, DCM and 1,2 - DCE show a microenvironment more polar than that of aliphatic hydrocarbons. The behaviour of dichloromethane and 1,2 - DCE is similar for the three probes and very different than that observed in aliphatic hydrocarbons. The microenvironment that they offer in front of [Ru(bpy)(3)](2+) is considerably more polar than that corresponding to n-heptane, while in front of E-T(30) is less polar. The results obtained using [Ru(bpy)(3)](2+) are the more difficult to explain, since displacement towards more polar (in 1,2-DCE and DCM) or less polar (in benzene, cumene, TCE) media were observed.