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Structural Studies of Proton-Conducting Fluorous Block Copolymer Membranes

Structural Studies of Proton-Conducting Fluorous Block Copolymer Membranes. Barbara Frisken – SFU Physics Laurant Rubatat - University of Fribourg Ken Shi – NRC IFCI Steven Holdcroft – SFU Chemistry and NRC IFCI Olivier Diat – CEA Grenoble.

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Structural Studies of Proton-Conducting Fluorous Block Copolymer Membranes

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  1. Structural Studies of Proton-Conducting Fluorous Block Copolymer Membranes Barbara Frisken – SFU Physics Laurant Rubatat - University of Fribourg Ken Shi – NRC IFCI Steven Holdcroft – SFU Chemistry and NRC IFCI Olivier Diat – CEA Grenoble

  2. Two Series of Diblock CopolymersSeries #1 – Variable Sulfonation A B Poly(Vinylidene DiFluoride-co-Hexafluoropropylene) P(VDF-co-HFP) Sulfonated PolyStyrene sPS Sulfonation Rate 22% 1A 32% 1B 1C 40% 17,900 g/mol 8,000 g/mol

  3. Two Series of Diblock CopolymersSeries #2 – Variable sPS Length A B Poly(Vinylidene DiFluoride-co-Hexafluoropropylene) P(VDF-co-HFP) Sulfonated PolyStyrene sPS Degree of polymerization 2A 9 12.5 2B 2C 18 1000-2000 g/mol 25,000 g/mol

  4. Conductivity and TEM Z. Ken Shi Nafion (1C) (1B) (2C) (2B) (1A) (2A)

  5. Conductivity and TEM Z. Ken Shi 1A 1B Nafion (1C) 1C (1B) (2C) 2B (2B) (1A) (2A) 2C

  6. SANS Studies Sample Detector q Neutron Beam The scattered intensity is proportional to the product of a structure factor S(q) and a form factor P(q): where P(q) describes the shape of the scattering objects and S(q) describes the spatial distribution of these objects.

  7. Neutron Scattering Spectra – in D2O Series #1 – Partially Sulfonated Series #2 – Variable Length Peak #1 Peak #1 Peak #2 Peak #2 Series #1 – Two Peaks Peak #1  400 Å Peak #2  40 Å Slight shift of the peaks to small angles  size increasing with IEC. Series #2 – Two Peaks Peak #1  400 Å Peak #2  40 Å Peak #1 is less sharp less ordered

  8. Contrast Variation Series #1 – Partially Sulfonated Series #2 – Variable Length Peak #1 Peak #2 Membrane 1C Peak #1 Peak #2 Membrane 2B

  9. Contrast Variation Series #1 Peak #1 Peak #2 Membrane 1C Ternary System Binary System Structure enhanced or diminished Match core Match corona

  10. Spectra Divisions Core-shell disk form factor R >> t + 2s => Lamellar Membrane 1C r t s

  11. Series #1 – Partially sulfonated PS Hydrated sPS PVDF Solvent pool 1A p = 56 % 30 Å 170 Å 180 Å 1B p = 30 % 220 Å 180 Å 28 Å 1C p = 25 % 165 Å 280 Å 25 Å

  12. Series #2 – Fully sulfonated Contrast Variation Binary System Structure enhanced or diminished Peak #1 Peak #2 Membrane 2B

  13. Small Length Scale Structure Hydrated sPS domain Modified hard-sphere model Yarusso and Cooper, Macromolecules 1983 Spherical ionic aggregates within PS matrix Increasing sulfonation from 22-100% leads to a decrease in the size of the barrier between ionic groups – consistent with improved conductivity.

  14. Series #1 Fluorous domains and Hydrated sPS domains Solvent pools in a PS matrix Series #2 400 Å 40 Å

  15. Compare to diblock copolymer theory Matsen and Bates, Macromolecules 1996 Series #1 QIm3m spheres H cylinders Series #2 QIa3d bi-continuous L lamellar f Volume fraction of A block (from data) N  Interaction between blocks (not known) Series #1 shows lamellar structure Series #2 shows phase separation, but no long range order

  16. Conductivity and SANS 1A Nafion 2C (1C) (1B) (2C) (2B) (1A) (2A) Large scale structure is more ordered in Series #1 sPS domains are similar Large scale structure affects the integrity of the membrane, but not the conductivity

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