title: Optimum tail length of fluorinated double-tail anionic surfactant for water/supercritical CO2 microemulsion formation.
abstract: The effect of surfactant tail structure on the stability of a water/supercritical CO2 microemulsion (W/scCO2 muE) was examined for various fluorinated double-tail anionic surfactants of different fluorocarbon chain lengths, F(CF2)n (n = 4, 6, 8, and 10), and oxyethylene spacer lengths, (CH2CH2O)(m/2) (m = 2 and 4). The phase behavior of the water/surfactant/CO2 systems was studied over a wide range of CO2 densities from 0.70 to 0.85 g/cm(3) (temperatures from 35 to 75 degrees C and pressures up to 500 bar) and corrected water-to-surfactant molar ratios (W0c). All of the surfactants yielded a W/scCO2 muE phase, that is, a transparent homogeneous phase with a water content larger than that permitted by the solubility of water in pure CO2. With increasing W0c, a phase transition occurred from the muE phase to a macroemulsion or a lamella-like liquid crystal phase. The maximum W0c value was obtained at a tail length of 12-14 A, indicating the presence of an optimum surfactant tail length for W/scCO2 muE formation.
authors.affiliation: Department of Materials Science and Technology, Faculty of Science and Technology, Hirosaki University, Bunkyo-cho 3, Hirosaki, Aomori 036-8561, Japan.
authors.forename: Masanobu
authors.initials: M
authors.lastname: Sagisaka
authors.forename: Daisuke
authors.initials: D
authors.lastname: Koike
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yoda
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Takebayashi
authors.forename: Takeshi
authors.initials: T
authors.lastname: Furuya
authors.forename: Atsushi
authors.initials: A
authors.lastname: Yoshizawa
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: D000838:Anions / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry*; D004655:Emulsions; D005030:Ethylenes / Q000737:chemistry; D005461:Fluorine / Q000737:chemistry*; D005466:Fluorocarbons / Q000737:chemistry; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry; D013501:Surface-Active Agents / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D000838:Anions; D004655:Emulsions; D005030:Ethylenes; D005466:Fluorocarbons; D013501:Surface-Active Agents; D014867:Water; D002245:Carbon Dioxide; D005461:Fluorine; D010100:Oxygen