Phase behavior of water-in-supercritical carbon dioxide microemulsion with sodium salt of bis(2,2,3,3,4,4,5,5-octafluoro-1-pentanol) sulfosuccinate

The fluorinated analogues of AOT surfactant, sodium salt of bis(2,2,3,3,4,4,5,5-octafluoro-1-pentanol) sulfosuccinate, which has CO2-philic chains and a hydrophilic head group, was synthesized for forming water-in-CO2 microemulsion. The cloud point of this surfactant was measured and the supercritical fluid-phase behavior of water-in-CO2 microemulsion was investigated by using a variable-volume view cell apparatus. It was found that the phase behavior of microemulsion is affected by the concentrations of water and surfactant in CO2, molar ratio of water to surfactant (Wo = [water]/[surfactant]), and the amount of CO2. From this experiment, we found out another cloudy point which exists above the homogeneous microemulsion region. We defined this point as “upper cloud point” and general cloud point as “lower cloud point. The region which exists between these two cloud points was defined as “stable region of microemulsion”. Conditions for the formation of water-in-CO2 microemulsion were obtained at temperatures up to 370.15 K.