title: New Class of Amphiphiles Designed for Use in Water-in-Supercritical CO2Microemulsions.
abstract: Water-in-supercritical CO2microemulsions formed using the hybrid F-H surfactant sodium 1-oxo-1-[4-(perfluorohexyl)phenyl]hexane-2-sulfonate, FC6-HC4, have recently been shown to have the highest water-solubilizing power ever reported. FC6-HC4 demonstrated the ability to outperform not only other surfactants but also other FCm-HCn analogues containing different fluorocarbon and hydrocarbon chain lengths (Sagisaka, M. et al. Langmuir 2015, 31, 7479-7487). With the aim of clarifying the key structural features of this surfactant, this study examined the phase behavior and water/supercritical CO2aggregate formation of 1-oxo-1-[4-(perfluorohexyl)phenyl]hexane (Nohead FC6-HC4), which is an FC6-HC4 analogue but now, interestingly, without the sulfonate headgroup. Surprisingly, Nohead FC6-HC4, which would not normally be identified as a classic surfactant, yielded transparent single-phase W/CO2microemulsions with polar cores able to solubilize a water-soluble dye, even at pressures and temperatures so low as to approach the critical point of CO2(e.g., ∼100 bar at 35 °C). High-pressure small-angle scattering (SANS) measurements revealed the transparent phases to consist of ellipsoidal nanodroplets of water. The morphology of these droplets was shown to be dependent on the pressure, Nohead FC6-HC4 concentration, and water-to-surfactant molar ratio. Despite having almost the same structure as Nohead FC6-HC4, analogues containing both shorter and longer hydrocarbons were unable to form W/CO2microemulsion droplets. This shows the importance of the role of the hydrocarbon chain in the stabilization of W/CO2microemulsions. A detailed examination of the mechanism of Nohead FC6-HC4 adsorption onto the water surface suggests that the hexanoyl group protrudes into the aqueous core, allowing for association between the carbonyl group and water.
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: Shunsuke
authors.initials: S
authors.lastname: Ogiwara
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: ISIS-CCLRC, Rutherford Appleton Laboratory , Chilton, Oxon OX11 0QX, U.K.
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Rogers
authors.affiliation: ISIS-CCLRC, Rutherford Appleton Laboratory , Chilton, Oxon OX11 0QX, U.K.
authors.forename: Richard K
authors.initials: RK
authors.lastname: Heenan
authors.affiliation: School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, U.K.
authors.forename: Ci
authors.initials: C
authors.lastname: Yan
authors.affiliation: School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, U.K.
authors.forename: Jocelyn Alice
authors.initials: JA
authors.lastname: Peach
authors.affiliation: School of Chemistry, University of Bristol , Cantock's Close, Bristol BS8 1TS, U.K.
authors.forename: Julian
authors.initials: J
authors.lastname: Eastoe