Preparation of a W/scCO₂ Microemulsion Using Fluorinated Surfactants

Abstract

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.

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

“…high diffusivity 49 increasing frequency of µE-droplet aggregation/separation) 20,48 . For the surfactant/W/CO2 mixtures be thermodynamically stable microemulsions (energy-minimum equilibrium state), longer equilibration might be necessary (> 1 hour) than employed in this study (~5 min owing to expense of SANS time) 24 , even though clear single phases have already appeared. The limited equilibration time in this experiment may be one reason for the higher polydispersity.…”

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

“…Regarding the volume and length of the surfactant tails, studies using double chain anionic surfactants have been devoted to the effect of structural modifications on the surfactant chain with limited surface tension ability, w/c phase stability, and surfactant solubilising power [15,[23][24][25][26][27]. Branching, methylation, and fluorination of the chain tips have been shown to decrease intermolecular interactions between the surfactant tails and produce more favourable tail-CO2 interactions which improve the CO2 compatibility [28,29].…”

Effect of surfactant headgroup on low-fluorine-content CO2-philic hybrid surfactants

“…A similar procedure has also been used by other groups dealing with CO2-philic surfactants [25,27,36,37]. To obtain comparable results, the surfactant concentration was fixed at 0.24 mol% (~0.05 mol dm -3 ).…”

“…Studies using double chain anionic surfactants have been devoted to the effect of structural modifications of the surfactant chains with limited surface tension ability, w/c phase stability, and surfactant solubilizing power [15,[23][24][25][26][27]. Branching, methylation, and fluorination of the chain tips have been shown to induce more favorable tail-CO2 interactions which improve CO2 compatibility [28,29].…”