Surfactant-Mixing Effects on the Interfacial Tension and the Microemulsion Formation in Water/Supercritical CO₂ System

Abstract

The effects of surfactant mixing on interfacial tension and on microemulsion formation were examined for systems of air/water and water/supercritical CO2 (scCO2) interfaces and for water/scCO2 microemulsions. A fluorinated surfactant, sodium bis(1H,1H,2H,2H-heptadecafluorodecyl)-2-sulfosuccinate (8FS(EO)2), was mixed with the three hydrocarbon surfactants, Pluronic L31, Tergitol TMN-6, and decyltrimethylammonium chloride (DeTAC), at equimolar ratio. For all the cases, the interfacial tension was significantly lowered by the mixing. The positive synergistic effect suggests that the mixed surfactants tend to pack more closely on the interface than the pure constituents. It was found, however, that the microemulsion formation in scCO2 was never facilitated by the mixing, except for the case of TMN-6. This is probably due to the segregation of the surfactants into hydrocarbon-rich and fluorocarbon-rich phases on the microemulsion surface.

Economical and Efficient Hybrid Surfactant with Low Fluorine Content for the Stabilisation of Water-in-CO2 Microemulsions

“…All measurements were performed at 25°C until the surface tension of the aqueous surfactant solutions reached constant values. Detailed information of the experimental procedures and apparatus are described elsewhere [36,43]. The critical micelle concentrations (cmc) of each surfactant solution were obtained from the intersection of the graph of the surface tension (γ) versus ln of concentration (ln c).…”

Nanostructures in Water-in-CO2 Microemulsions Stabilized by Double-Chain Fluorocarbon Solubilizers

“…[3][4][5][6][7][8][9] However, most commercial and known hydrocarbon surfactants are insoluble and inactive in scCO2 systems 3 . In this regard, it became apparent that conventional surfactant-design theory cannot be applied to W/CO2 systems directly, and that CO2-philicity is not directly comparable to 4 oleo-philicity.…”

Characterization of Water/Supercritical CO2 Microemulsion by UV-visible Spectroscopy and Dynamic Light Scattering

“…However, only a few have succeeded in developing a W/scCO 2 mE with W 0 c > 0 (W 0 c :water-to-surfactant molar ratio corrected by subtracting the moles of water soluble in CO 2 ). In a previous work [20][21][22][23][24][25][26][27] , we synthesized fluorinated Aerosol-OT (AOT) analogue surfactants and examined their ability to stabilize W/scCO 2 mEs. We found that a fluorinated AOT-analogue surfactant, sodium bis(1H,1H,2H,2H-heptadecafluorodecyl)-2 -sulfosuccinate (8FS(EO) 2 ), successfully stabilized a transparent single-phase Winsor-IV W/scCO 2 mE (IV mE) with a W 0 c value of 32.…”

“…The W 0 c value of 32 is extremely large compared to those previously reported for other W/scCO 2 mE systems . On the other hand, the IV mE became a turbid W/scCO 2 macroemulsion (E) with decreasing pressure, and then it turned into a Winsor-I-or Winsor-II-mE-like two-phase (2Ø) when magnetic stirring was stopped [20][21][22][23][24][25][26][27][28] . In this case, the Winsor-I and -II mean scCO 2 /W mE with a separated excess scCO 2 and W/scCO 2 mE with a separated excess water, respectively 28) .…”