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

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 (W0total=11.5, and W0corr=6.0) 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.