Abstract
A study has been made on the effect of the organic solvent upon the properties of the interface of reverse micelles formed by sodium bis (2-ethylhexyl) sulfosuccinate (AOT) - water. The study has been performed using fluorescence and absorption spectroscopies. The probes considered were 8-anilinonaphtha lene-1-sulfonate (ANS-) and ruthenium tris [(bipyridine)]2+, [Ru (bpy)3]2+, in fluorescence spectroscopy, and ET(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 (ET (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, chlorobenzene, 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 ET(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
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