| Abstract
| - The stability of water-in-CO2 (W/C) emulsions stabilized with poly(dimethylsiloxane)-b-poly(methacrylic acid) (PDMS-b-PMA) and PDMS-b-poly(acrylic acid) (PDMS-b-PAA) ionomersurfactants is reported as a function of surfactant architecture, pH, temperature, pressure, anddroplet flocculation. For a given PDMS block length, the stability of the emulsion is correlatedwith the distance from the balanced state where the surfactant prefers the water and CO2 phasesequally. When the pH starting at 3 is raised up to 5−6, the hydrophilic/CO2-philic balance ofthe surfactant increases, because of ionization of COOH, and the emulsion becomes more stable.At the pH of maximum stability, the emulsion becomes more stable with a decrease in the PDMSlength, for a given ratio of block lengths, because of gelation of the flocculated 2−5 μm primarydroplets. W/C emulsions are stable with respect to sedimentation for >24 h and are resistant tocoalescence for more than 7 days. Because of gelation, the W/C emulsions are more stable thanwater/hexane emulsions (at ambient pressure) formed at the same conditions. The addition of20% hexane to CO2 as a cosolvent reduced flocculation in some cases to zero.
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