Micropolarity of sodium bis(2-ethylhexyl) sulfosuccinate reverse micelles prepared in supercritical ethane and near-critical propane

The micropolarity of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelles prepared in supercritical ethane and near-critical propane has bee n determined in terms of a solvent polarity parameter, E-T(30) values, by u sing absorption probes, 1-ethyl-4-methoxycarbonyl pyridinium iodide and 2,6 -diphenyl-4-(2,4,6-triphenylpyridinio)-phenolate as a functions of pressure and the molar ratio of water to AOT, W-0, at a constant temperature of 310 K. The micropolarity comparable to that of ethanol was observed for revers e micelles containing water of W-0 = 2, The micropolarity increased with th e water content and became independent of pressure after the system changed to a one-phase reverse micelle solution. For a given W-0 value, no differe nce in the micropolarity was noticed in the micelles prepared in ethane and propane. Phase behaviour investigations have revealed that complete dissol ution of 50 mM AOT occurred at 20 MPa in supercritical ethane, while a much lower pressure of MPa was required in near-critical propane. The amount of water solubilized in reverse micelles formed in supercritical ethane was r elatively low, reaching a W-0 value of 7 at 36 MPa. In contrast, the amount of water solubilized in near-critical propane reverse micelles was W-0 = 1 1 at a much lower pressure of 6 MPa. A higher pressure was required to solu bilize larger amount of water in reverse micelles prepared in both ethane a nd propane.