title: Properties of surfactant films in water-in-CO2 microemulsions obtained by small-angle neutron scattering.
abstract: OBJECTIVE
  The formation, stability and structural properties of normal liquid phase microemulsions, stabilized by hydrocarbon surfactants, comprising water and hydrocarbon oils can be interpreted in terms of the film bending rigidity (energy) model. Here, this model is tested for unusual water-in-CO2 (w/c) microemulsions, formed at high pressure with supercritical CO2 (sc-CO2) as a solvent and fluorinated surfactants as stabilizers. Hence, it is possible to explore the generality of this model for other types of microemulsions.
  
  
  METHODS
  High Pressure Small-Angle Neutron Scattering (HP-SANS) has been used to study w/c microemulsions, using contrast variation to highlight scattering from the stabilizing fluorinated surfactant films: these data show clear evidence for spherical core-shell structures for the microemulsion droplets.
  
  
  RESULTS
  The results extend understanding of w/c microemulsions since previous SANS studies are based only on scattering from water core droplets. Here, detailed structural parameters for the surfactant films, such as thickness and film bending energy, have been extracted from the core-shell SANS profiles revealed by controlled contrast variation. Furthermore, at reduced CO2 densities (∼0.7gcm(-3)), elongated cylindrical droplet structures have been observed, which are uncommon for CO2 microemulsions/emulsions. The implications of the presence of cylindrical micelles and droplets for applications of CO2, and viscosity enhancements are discussed.
authors.affiliation: School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom.
authors.forename: Ci
authors.initials: C
authors.lastname: Yan
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.affiliation: Department of Materials Science and Technology, Faculty of Science and Technology, Hirosaki University, Bunkyo-cho 3, Hirosaki, Aomori 036-8561, Japan.
authors.forename: Craig
authors.initials: C
authors.lastname: James
authors.affiliation: Rutherford Appleton Laboratory, ISIS Facility, Chilton, Oxfordshire OX11 0QX, United Kingdom.
authors.forename: Sarah
authors.initials: S
authors.lastname: Rogers
authors.affiliation: Swansea University, Singleton Park, Swansea SA2 8PP, United Kingdom.
authors.forename: Shirin
authors.initials: S
authors.lastname: Alexander
authors.affiliation: School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom. Electronic address: Julian.eastoe@bris.ac.uk.
authors.forename: Julian
authors.initials: J
authors.lastname: Eastoe
keywords: Film bending rigidity; Fluorinated surfactants; Microemulsions; Small-angle neutron scattering; Supercritical CO(2)