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.

Gas-Expanded Liquids

“…Expansion of mixtures of perfluoropolyether oil, water, and a surfactant by CO 2 has been shown to trigger the formation of microemulsions . The surfactant was [Cl{CF 2 CF(CF 3 )O} n CF 2 CO 2 - ]NH 4 ( n ≈ 3).…”

“…Expansion of mixtures of perfluoropolyether oil, water, and a surfactant by CO 2 has been shown to trigger the formation of microemulsions. 162 The surfactant was [Cl{CF 2 CF-(CF 3 )O} n CF 2 CO 2 -]NH 4 (n ≈ 3). The mixture composition was typically 5 wt % surfactant in the oil, with a 20:1 water/ surfactant mole ratio.…”

Fluoropolymer Synthesis in Carbon Dioxide-Expanded Liquids: A Practical Approach to Avoid the Use of Perfluorooctanoic Acid

“…As we have shown, the solvent quality of C0 2 can be improved through the use of co-solvents. The utility of carbon dioxide can also be expanded through the use of surfactants, however, for pure C0 2 , this usually demands specially designed surfactants that contain a "C0 2 -philic" domain such as fluorinated (4,(26)(27)(28)(29), siloxane (30,31), and some hydrocarbon compounds with special structures (32)(33)(34). Using the CXL system, such as the C0 2 -expanded acetic acid used in this study, we expected a wider polarity range could be obtained (10) which in turn should substantially alter the interaction between C0 2 and conventional surfactants.…”

Molecular and phase toxicity of compressed and supercritical fluids in biphasic continuous cultures ofClostridium thermocellum

“…The instrument was fitted with a high-pressure variable volume spectroscopic cell (rated to 20.7 MPa, working volume of 10 -25 mL) with a light path of 2.5 cm (see Kho et al, 2004 for a description of the spectroscopic cell). Experiments were initiated by loading the spectroscopic cell with a microbial cell suspension and heating to 333 K. Substrate and yeast extract was excluded from the suspension to prevent cell growth, thus eliminating the need to quantify the effects of growth on interfacial adsorption.…”