Affiliations 

  • 1 Department of Frontier Materials Chemistry, Graduate School of Science and Technology, Hirosaki University, 3 Bunkyo-cho, Hirosaki, Aomori 036-8561, Japan. Electronic address: sagisaka@hirosaki-u.ac.jp
  • 2 Department of Frontier Materials Chemistry, Graduate School of Science and Technology, Hirosaki University, 3 Bunkyo-cho, Hirosaki, Aomori 036-8561, Japan
  • 3 Department of Chemistry, Faculty of Science and Mathematics, Universiti Pendidikan Sultan Idris, 35900 Tanjong Malim, Perak, Malaysia; Nanotechnology Research Centre, Faculty of Science and Mathematics, Universiti Pendidikan Sultan Idris, 35900 Tanjong Malim, Perak, Malaysia
  • 4 Univ. Cote d'Azur, NICE-Lab,61-63 av. S. Viel, 06200 Nice, France
  • 5 Department of Chemical and Petroleum Engineering, University of Pittsburgh, 940 Benedum Hall, 3700 O'Hara Street, Pittsburgh, PA 15261, United States
  • 6 ISIS-CCLRC, Rutherford Appleton Laboratory, Chilton, Oxon OX11 0QX, UK
  • 7 School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK
  • 8 School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK. Electronic address: Julian.Eastoe@bristol.ac.uk
Colloids Surf B Biointerfaces, 2018 Aug 01;168:201-210.
PMID: 29276082 DOI: 10.1016/j.colsurfb.2017.12.012

Abstract

Previous work (M. Sagisaka, et al. Langmuir 31 (2015) 7479-7487), showed the most effective fluorocarbon (FC) and hydrocarbon (HC) chain lengths in the hybrid surfactants FCm-HCn (sodium 1-oxo-1-[4-(perfluoroalkyl)phenyl]alkane-2-sulfonates, where m = FC length and n = HC length) were m and n = 6 and 4 for water solubilization, whereas m 6 and n 6, or m 6 and n 5, were optimal chain lengths for reversed micelle elongation in supercritical CO2. To clarify why this difference of only a few methylene chain units is so effective at tuning the solubilizing power and reversed micelle morphology, nanostructures of water-in-CO2 (W/CO2) microemulsions were investigated by high-pressure small-angle neutron scattering (SANS) measurements at different water-to-surfactant molar ratios (W0) and surfactant concentrations. By modelling SANS profiles with cylindrical and ellipsoidal form factors, the FC6-HCn/W/CO2 microemulsions were found to increase in size with increasing W0 and surfactant concentration. Ellipsoidal cross-sectional radii of the FC6-HC4/W/CO2 microemulsion droplets increased linearly with W0, and finally reached ∼39 Å and ∼78 Å at W0 = 85 (close to the upper limit of solubilizing power). These systems appear to be the largest W/CO2 microemulsion droplets ever reported. The aqueous domains of FC6-HC6 rod-like reversed micelles increased in size by 3.5 times on increasing surfactant concentration from 35 mM to 50 mM: at 35 mM, FC6-HC5 formed rod-like reversed micelles 5.3 times larger than FC6-HC6. Interestingly, these results suggest that hybrid HC-chains partition into the microemulsion aqueous cores with the sulfonate headgroups, or at the W/CO2 interfaces, and so play important roles for tuning the W/CO2 interfacial curvature. The super-efficient W/CO2-type solubilizer FC6-HC4, and the rod-like reversed micelle forming surfactant FC6-HC5, represent the most successful cases of low fluorine content additives. These surfactants facilitate VOC-free, effective and energy-saving CO2 solvent systems for applications such as extraction, dyeing, dry cleaning, metal-plating, enhanced oil recovery and organic/inorganic or nanomaterial synthesis.

* Title and MeSH Headings from MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.