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Formation of water (W) in supercritical carbon dioxide (scCO2) (W/scCO2) type microemulsions was examined using four hybrid surfactants, the sodium 1-oxo-1-[4-(tridecafluorohexyl)phenyl]-2-alkanesulfonates (FC6-HCn, n ) 2, 4, 6, and 8), which have a hydrocarbon chain of different length and a fluorocarbon chain in one molecule and an Aerosol-OT (AOT) analogue fluorinated twin tail type surfactant, sodium bis(1H,1H,2H,2H-heptadecafluorodecyl)-2-sulfosuccinate (8FS(EO) 2). For comparison AOT was also used. The hybrid type surfactants (FC6-HCn) gave a transparent single phase, identified as a W/scCO2 microemulsion, with a water-to-surfactant molar ratio, W0 c < 7, irrespective of hydrocarbon chain length. The fluorinated AOT analogue also yielded a transparent single phase, again identified as a W/scCO2 microemulsion, with a W0 c value close to 32sone of the highest ever reported. The aqueous core in the 8FS(EO)2 reversed micelle was examined by FT-IR spectra using D2O. The spectra revealed that the aqueous core swells on addition of water and shrinks with increase in pressure. The remarkable ability of 8FS(EO) 2 to form a W/scCO2 microemulsion would be brought about by its high adsorption capacity and its excellent facility to lower the water/scCO2 interfacial tension, in addition to a low interaction and strong steric repulsion between its CO2-philic groups.

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The adsolubilization of styrene, isoprene, and mixtures of styrene and isoprene into cetyltrimethylammonium bromide (CTAB) bilayers (admicelles) on precipitated silica is investigated. The results show that the styrene adsolubilization constant is nearly unchanged with increasing styrene equilibrium concentration in the aqueous phase, while the isoprene adsolubilization constant increases with increasing isoprene partial pressure. The adsolubilization constants suggest that styrene adsolubilizes into both the palisade layer and the core of the admicelle, while isoprene adsolubilizes into the palisade layer. In the co-monomer system styrene adsolubilization is slightly increased in the presence of isoprene but isoprene adsolubilization is significantly enhanced in the presence of styrene; however, the adsolubilization isotherms of both monomers have increasing slopes in the co-monomer system and show that there is a synergistic effect, possibly due to swelling of the admicelle due to the addition of adsolubilizate.

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