Micropolarity of Reverse Micelles of Aerosol-OT in n-Hexane

Abstract

The microenvironment of the polar core of reverse micelles of the anionic surfactant AOT in n-hexane was studied by following the solvatochromic behavior of 1-methyl-8-oxyquinolinium betaine (QB) and ET(30). A solvatochromic study in pure solvents shows that QB presents two bands which could indicate two different effects. The band in the visible region, B1, which is the band for charge transfer from oxygen to nitrogen, is sensitive, mainly of polarity. The band in the UV region, B2, is most sensitive to the hydrogen bond donor capability of the solvent and it is assigned to the charge transfer of the phenoxide to the ring. These properties are used to establish changes in the probe microenvironment within the reverse micelles. The studies made by varying AOT concentration and the water content of the micellar solution show that QB resides in the micelle interface, indicating its polarity and its hydrogen bond donor ability. These properties at the interface of the AOT micelles in n-hexane increase up to W = 10 and then are practically constant, as demonstrated by the shifts and intensity variations of the B1 and B2 bands with W at a constant AOT concentration. Similar results are obtained with ET(30). However, because the latter is a much more voluminous probe, it is believed to disrupt the system, indicating different places within the micelle than QB.