The Nature and Structure of Water/AOT/Ethane (W/O) Microemulsion under Supercritical Conditions Studied by High-Pressure FT-IR Spectroscopy

High-pressure FT-IR spectroscopy was used to study a W/O microemulsion system of AOT micelles dispersed in supercritical ethane. The system was found to be in a single-phase state depending on the pressure (P), temperature (T), and water-to-AOT molar ratio (W0). The number of water molecules that the AOT micelles were able to solubilize reached about 15 at 35.0 MPa and 343.1 K. This presents a striking contrast to AOT micelles in ordinary organic liquids, in which the number of solubilized water molecules ranges from 2 to 6. The solubilized water molecules were present in three different types and their relative quantities depended on W0, P, and T. The presence of trans-like and/or gauche-like AOT isomers also depended on the operating variables, which affected the interactions between AOT molecules and the water molecules solubilized in them. The solubilization of water and the rotational isomerism of AOT were significantly influenced in different ways by the addition of salts, including lithium chloride, guanidine hydrochloride, and cesium iodide.