Investigation of AOT reverse microemulsions in supercritical carbon dioxide

Bis(2-ethylhexyl) sodium sulphosuccinate (AOT) was successfully solubilised in supercritical carbon dioxide (scCO(2)), with ethanol or pentanol as co-solvent. Three molecular spectroscopic probes: methyl orange (MO), 8-hydroxy-1,3,6-pyrenetrisulphonic acid trisodium salt (HPTS), and riboflavin (RF) were used to examine the solubilisation characteristics of the water/scCO(2) microemulsions formed with AOT. MO was extracted at various operating conditions, although the wavelength of its solvatochromic absorption maximum was not indicative of bulk water properties. Instead, the spectral results imply that MO may be located at the surfactant/water interface. The highly water-soluble dye HPTS was unable to be extracted into scCO(2)/AOT/water systems, suggesting that the water in the reverse micelle core was not as polar under supercritical conditions as those at ambient conditions. Finally, RF was extracted into the supercritical phase (40 degrees C, 175 bar) with pentanol co-solvent, with an apparent enhanced uptake compared with the value at 40 degrees C and ambient pressure in bulk water. This appears to be due to the presence of microcrystals dispersed in the supercritical phase. (C) 1999 Elsevier Science B.V. All rights reserved.