A SMALL-ANGLE NEUTRON-SCATTERING STUDY OF WATER IN CARBON-DIOXIDE MICROEMULSIONS

Phase behavior and small angle neutron scattering (SANS) experiments w ere performed on mixtures of D2O/CO2/ammonium carboxylate perfluoropol yether (PFPE) surfactant as a function of pressure (192-287 bar) and D 2O composition (0.8-2.0 wt %) at 35 degrees C. SANS measurements provi ded direct evidence of water-swollen inverted micelles in CO2. At a co nstant PFPE concentration of 2.1 wt % in CO2, the microemulsion core r adius increased from 20 to 36 Angstrom as the D2O concentration increa sed from 0.8 to 2.0 wt %. For a constant water concentration, paramete rs extracted from model fits of the SANS spectra indicated that as the phase boundary was approached on reducing pressure, micellar structur e remained essentially unchanged, while critical fluctuations increase d.