| Microemulsions of water-in-supercritical carbon dioxide (w/c) were investigated by high pressure Nuclear Magnetic Resonance (NMR) spectroscopy. These systems hold promise as reaction media for conducting homogenous catalytic reactions.;Perfluoropropylene oxide ammonium carboxylate oligomers were used as surfactants, and a probe salt, ammonium hexafluorophosphate (AHFP), was used to investigate micelle formations and structure. The first observation of spontaneous microemulsion formations in w/c systems is reported herein. The spontaneous micelle formation provides critical evidence of thermodynamically stable microemulsions. A NMR imaging technique, utilizing toroid cavity detectors, provides images of the hexafluorophosphate anion uniformly dispersed throughout the carbon dioxide phase. Negative Nuclear Overhauser Effects (NOE) were used to probe dipole-dipole interactions between the AHFP anion and the surfactant's carboxylate head group. The NOE provides evidence of short range interactions between the two anions in an ordered environment, indicating their location in the charge double layer at the micellar interface. |
