title: Phase behavior of CO2-expanded fluorinated microemulsions.
abstract: The formation of CO2-expanded, fluorinated reverse microemulsions is demonstrated for the system of perfluoropolyether (PFPE) surfactant (ClPFPE-NH4, MW = 632) and PFPE oil (PFPE, MW = 580). The phase behavior of this system is examined as a function of temperature (25-45 degrees C), pressure, CO2 concentration, and water to surfactant molar ratios (W0 = 10 and 20). Visual observations of one-phase behavior consistent with reverse microemulsion formation are further supported by spectroscopic measurements that establish the existence of a bulk water environment within the aqueous core. Microemulsion formation is not observed in the absence of CO2 for this PFPE surfactant/PFPE oil system, and a CO2 content greater than 70 mol % is required to induce microemulsion formation. Over the range of water loadings and temperatures investigated, the lowest cloud point pressure is observed at 46 bar (5 wt % ClPFPE-NH4 in PFPE oil, W0 = 20, xCO2 = 0.7, T = 25 degrees C). In the regions where one-phase behavior is observed, the cloud point pressures increase with temperature, water loadings, and CO2 content. The driving forces of microemulsion formation in the CO2-expanded fluorinated solvent are discussed relative to traditional reverse microemulsions and CO2-continuous microemulsions.
authors.affiliation: Department of Chemical & Materials Engineering, University of Kentucky, Lexington, Kentucky 40506-0046, USA.
authors.forename: Yeh Wei
authors.initials: YW
authors.lastname: Kho
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Conrad
authors.forename: Barbara L
authors.initials: BL
authors.lastname: Knutson
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry*; D004655:Emulsions; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry*; D044367:Phase Transition; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D004655:Emulsions; D006845:Hydrocarbons, Fluorinated; D013501:Surface-Active Agents; D014867:Water; D002245:Carbon Dioxide