Determination of the Water/AOT/Isooctane Reverse Micelles Size Parameters from Their Refractive Index Data

The present paper aims to study the proprieties of water confined in water/AOT/isooctane reverse micelles from their refractive indices at 298.5 K. The refractive indices of the microemulsions were investigated at increasing water concentration and at different micellar volume fractions, Φd. The refractive index of micellar water was deduced for a large water to AOT molar ratio, W0. The refractive index of interfacial water was also calculated. Then, the molar faction of interfacial water, α, was deduced for different W0 values and compared with those measured by NMR as reported in the literature. The results show qualitative agreement. Finally, the average aggregation number, nagg, the area per surfactant headgroup, σ, as well as the interfacial thickness, di, of the reverse micelles were determined for the W0 values studied. The values of these structural parameters also show good qualitative agreement with NMR and small angle X-ray scattering data reported in the literature. Thus, the refractive index method can be a cheap and fast alternative for these two methods.