WATER-STRUCTURE IN WATER AOT N-HEPTANE MICROEMULSIONS BY FT-IR SPECTROSCOPY

FT-IR spectra in the OH stretching region of water/sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/n-heptane microemulsions as a function of the water/AOT molar ratio (R) and of the weight fraction (φ) of the micellar phase have been recorded at 25°C. After elimination of the unwanted CH contribution and correction for the water concentration, the shape of the normalized OH bands has been found to be dependent on R and practically independent of φ. The analysis of these bands in terms of "bound" and "bulk" water (representing, as a first approximation, the two water domains within the water pool) allowed the evaluation of the fraction (α) of the "bound" water as a function of R. At each R, α was found to be nearly the same for percolated and unpercolated microemulsions. This suggests that the water/AOT/n-heptane microemulsions well above the percolation threshold are still formed by water-containing AOT reversed micelles dispersed in the oil phase. © 1992.