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 (W_o = 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.