Micellization of sodium bis(2-ethylhexyl)sulfosuccinate in supercritical CO2 with fluorinated co-surfactant and its solubilization of hydrophilic species

Supercritical Fluid Research Center, National Institute of Advanced Industrial Science and Technology, 4-2-1 Nigatake, Miyagino-ku, Sendai 983-8551, Japan; CREST, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi 332-0012, Japan; Revised 12 July 2004. Accepted 21 July 2004. Available online 17 September 2004.
The Journal of Supercritical Fluids 01/2005; DOI: 10.1016/j.supflu.2004.07.006

ABSTRACT The solubilities of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) in supercritical CO2 (scCO2) in the presence of ethanol, 1-pentanol and 2,2,3,3,4,4,5,5-octafluoro-1-pentanol (F-pentanol) at 38.0 °C and different pressures were determined. It was found that AOT (0.01–0.07 M) could be solubilized in scCO2 with smaller amount of F-pentanol (0.20–0.30 M) compared with ethanol (1.00–1.40 M) and 1-pentanol (0.60–1.00 M), because F-pentanol has ‘CO2-philic’ fluorinated alkane chain. The phase behavior studies for AOT (0.03 M)/F-pentanol (0.18–0.35 M)/scCO2 system ranging in temperature from 38.0 to 52.2 °C and pressures up to 35.00 MPa indicated that the cloud point pressure of AOT decreased significantly with the addition of F-pentanol, and the lower temperature, the lower cloud point pressure of AOT especially at higher concentrations of F-pentanol. In addition, 0.016 M AOT/0.24 M F-pentanol/scCO2 system could solubilize a significant amount of water (, and ) at moderate conditions, which implied the formation of water-in-CO2 reverse microemulsions. Visual observation using a video camera on the solubilization of methyl orange (MO) further proved the existence of polar micro-water domains within the AOT W/C reverse microemulsions. Besides that, bio-macromolecules such as cytochrome c and lysozyme and 8-hydroxy-1,3,6-pyrenetrisulphonic acid trisodium salt (HPTS) characteristic of highly ionic property could be solubilized in the microemulsions, which was obviously reflected by the UV–vis spectra.

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