title: Effect of Fluorocarbon and Hydrocarbon Chain Lengths in Hybrid Surfactants for Supercritical CO2.
abstract: Hybrid surfactants containing both fluorocarbon (FC) and hydrocarbon (HC) chains have recently been shown to solubilize water and form elongated reversed micelles in supercritical CO2. To clarify the most effective FC and HC chain lengths, the aggregation behavior and interfacial properties of hybrid surfactants FCm-HCn (FC length m/HC length n = 4/2, 4/4, 6/2, 6/4, 6/5, 6/6, and 6/8) were examined in W/CO2 mixtures as functions of pressure, temperature, and water-to-surfactant molar ratio (W0). The solubilizing power of hybrid surfactants for W/CO2 microemulsions was strongly affected by not only the FC length but also by that of the HC. Although the surfactants having short FC and/or HC tails (namely, m/n = 4/2, 4/4, and 6/2) did not dissolve in supercritical CO2 (even at ∼17 mM, ≤400 bar, temperature ≤ 75 °C, and W0 = 0-40), the other hybrid surfactants were able to yield transparent single-phase W/CO2 mixtures identified as microemulsions. The solubilizing power of FC6-HCm surfactants reached a maximum (W0 ∼ 80 at 45 °C and 350 bar) with a hydrocarbon length, m, of 4. The W0 value of 80 is the highest for a HC-FC hybrid surfactant, matching the highest value reported for a FC surfactant which contained more FC groups. High-pressure small-angle neutron scattering measurements from FCm-HCn/D2O/CO2 microemulsions were consistent with growth of the microemulsion droplets with increasing W0. In addition, not only spherical reversed micelles but also nonspherical assemblies (rodlike or ellipsoidal) were found for the systems with FC6-HCn (n = 4-6). At fixed surfactant concentration and W0 (17 mM and W0 = 20), the longest reversed micelles were obtained for FC6-HC6 where a mean aspect ratio of 6.3 was calculated for the aqueous cores.
authors.affiliation: †Department of Frontier Materials Chemistry, Graduate School of Science and Technology, Hirosaki University, 3 Bunkyo-cho, Hirosaki, Aomori 036-8561, Japan.
authors.forename: Masanobu
authors.initials: M
authors.lastname: Sagisaka
authors.affiliation: †Department of Frontier Materials Chemistry, Graduate School of Science and Technology, Hirosaki University, 3 Bunkyo-cho, Hirosaki, Aomori 036-8561, Japan.
authors.forename: Shinji
authors.initials: S
authors.lastname: Ono
authors.affiliation: †Department of Frontier Materials Chemistry, Graduate School of Science and Technology, Hirosaki University, 3 Bunkyo-cho, Hirosaki, Aomori 036-8561, Japan.
authors.forename: Craig
authors.initials: C
authors.lastname: James
authors.affiliation: †Department of Frontier Materials Chemistry, Graduate School of Science and Technology, Hirosaki University, 3 Bunkyo-cho, Hirosaki, Aomori 036-8561, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Yoshizawa
authors.forename: Azmi
authors.initials: A
authors.lastname: Mohamed
authors.affiliation: ∥Univ. Nice Sophia-Antipolis, CNRS, Equipe Surfaces et Interfaces, Parc Valrose, 06100 Nice, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Guittard
authors.affiliation: ⊥ISIS-CCLRC, Rutherford Appleton Laboratory, Chilton, Oxon OX11 0QX, United Kingdom.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Rogers
authors.affiliation: ⊥ISIS-CCLRC, Rutherford Appleton Laboratory, Chilton, Oxon OX11 0QX, United Kingdom.
authors.forename: Richard K
authors.initials: RK
authors.lastname: Heenan
authors.affiliation: #School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom.
authors.forename: Ci
authors.initials: C
authors.lastname: Yan
authors.affiliation: #School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom.
authors.forename: Julian
authors.initials: J
authors.lastname: Eastoe