title: Interfacial properties of branch-tailed fluorinated surfactants yielding a water/supercritical CO2 microemulsion.
abstract: We have examined the interfacial properties of several fluorinated surfactants in a water/CO2 mixture with a pendant drop tensiometer and revealed the relationships between the interfacial properties, the surfactant structure, and the microemulsifying power. We employed the following Aerosol-OT analogue surfactants that have two fluorinated tails: bis(1H,1H,5H-octafluoropentyl)-2-sulfosuccinate (di-HCF4), sodium bis(1H,1H,9H-hexadecafluorononyl)-2-sulfosuccinate (di-HCF8), sodium bis(1H,1H,2H,2H-heptadecafluorodecyl)-2-sulfosuccinate (8FS(EO)2), and sodium bis((1H,1H,2H,2H-heptadecafluorodecyl)-oxyethylene)-2-sulfosuccinate (8FS(EO)4). To discuss the effect of the fluorocarbon/hydrocarbon ratio in single surfactant molecules, water/CO2 interfacial tension (IFT) of a hybrid surfactant with one fluorocarbon and one hydrocarbon tail, that of a surfactant with a single fluorinated tail, and that of a hydrocarbon surfactant, Aerosol-OT (AOT), were examined. The hybrid surfactant employed was sodium 1-oxo-1-[4-(tridecafluorohexyl)phenyl]-2-hexanesulfonate (FC6-HC4), and the single-tailed surfactant was perfluoropolyether ammonium carboxylate (PFPECOONH4, CF3CF2(CF2OCF(CF3))4COONH4). All of the fluorinated AOT analogue surfactants exhibited an excellent level of activity at the water/CO2 interface compared with other fluorinated surfactants and AOT. With a larger hydrocarbon chain number in the CO2-philic tails (i.e., from 0 to 2), the IFT of the AOT analogue surfactants was increased. The area occupied by one surfactant molecule at the water/CO2 interface, A, and the critical microemulsion concentration, cmicroc, were determined and used to examine the water-to-surfactant molar ratio within a reversed micelle, W0c, of the surfactants. The surfactants that form W/scCO2 microemulsions with a large W0c were found to lower the interfacial tension efficiently irrespective of increases in temperature. To achieve the most desirable W0C, the surfactant needs not only a high CO2-philicity of the tails but also a high Krafft point, properties which induce a low hydrophilic/CO2-philic balance.
authors.affiliation: National Institute of Advanced Industrial Science and Technology, Institute for Green Technology, Higashi 1-1, Tsukuba, Ibaraki 305-8565, Japan.
authors.forename: Masanobu
authors.initials: M
authors.lastname: Sagisaka
authors.forename: Tatsunori
authors.initials: T
authors.lastname: Fujii
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Ozaki
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yoda
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Takebayashi
authors.forename: Yukishige
authors.initials: Y
authors.lastname: Kondo
authors.forename: Norio
authors.initials: N
authors.lastname: Yoshino
authors.forename: Hideki
authors.initials: H
authors.lastname: Sakai
authors.forename: Masahiko
authors.initials: M
authors.lastname: Abe
authors.forename: Katsuto
authors.initials: K
authors.lastname: Otake
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry*; D004655:Emulsions / Q000737:chemistry; D005461:Fluorine / Q000737:chemistry*; D005466:Fluorocarbons / Q000737:chemistry*; D015394:Molecular Structure; D013499:Surface Properties; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry*; D013696:Temperature; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D004655:Emulsions; D005466:Fluorocarbons; D013501:Surface-Active Agents; D014867:Water; D002245:Carbon Dioxide; D005461:Fluorine