Structural Studies of Proton-Conducting Fluorous Block Copolymer Membranes
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Structural Studies of Proton-Conducting Fluorous Block Copolymer Membranes
Barbara Frisken – SFU PhysicsLaurant Rubatat - University of FribourgKen Shi – NRC IFCISteven Holdcroft – SFU Chemistry and NRC IFCIOlivier Diat – CEA Grenoble
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Two Series of Diblock CopolymersSeries #1 – Variable Sulfonation
22%
32%
40%
Sulfonation Rate
1B
1A
1C
A BPoly(Vinylidene DiFluoride-co-Hexafluoropropylene)
P(VDF-co-HFP)Sulfonated PolyStyrenesPS
17,900 g/mol 8,000 g/mol
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9
12.5
18
2B
2A
2C
25,000 g/mol
Degree of polymerization
A BPoly(Vinylidene DiFluoride-co-Hexafluoropropylene)
P(VDF-co-HFP)Sulfonated PolyStyrenesPS
1000-2000 g/mol
Two Series of Diblock CopolymersSeries #2 – Variable sPS Length
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Conductivity and TEM Z. Ken Shi
(2A)(2B)
(1B)
(1A)
(2C)
(1C)Nafion
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Conductivity and TEM Z. Ken Shi
(2A)(2B)
(1B)
(1A)
(2C)
(1C)Nafion
1A
1B
1C
2B
2C
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SANS Studies
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.
I(q) K S(q) P(q)
Neutron Beam
Sample Detector
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Peak #1
Peak #2
Series #1 – Two PeaksPeak #1 400 ÅPeak #2 40 Å
Slight shift of the peaks to small angles size increasing with IEC.
Neutron Scattering Spectra – in D2O
Series #2 – Two PeaksPeak #1 400 ÅPeak #2 40 Å
Peak #1 is less sharp less ordered
Peak #2
Peak #1
Series #1 – Partially Sulfonated Series #2 – Variable Length
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Contrast Variation
Peak #1
Peak #2
Membrane 2B
Peak #1
Membrane 1C
Peak #2
Series #1 – Partially Sulfonated Series #2 – Variable Length
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ContrastVariationSeries #1
Peak #1
Peak #2
Binary System
Structure enhanced or diminished
Ternary System
Match core
Match corona
Membrane 1C
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Spectra Divisions
2
2
D O
divH O
I (q) K S(q)I (q)
I (q) 2D O
P (q)
K S(q)
2
2 2
D O
H O H O
P (q)
P (q) P (q)
Membrane 1C
ts
r
Core-shell diskform factorR >> t + 2s
=> Lamellar
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Series #1 – Partially sulfonated PVDF PSHydrated sPS
25 Å 165 Å280 Å
180 Å
220 Å
30 Å 170 Å
28 Å 180 Å
Solvent pool
1B
1A
1C
p = 56 %
p = 30 %
p = 25 %
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Series #2 – Fully sulfonatedContrast Variation
Peak #1
Peak #2
Membrane 2B
Binary System
Structure enhanced or diminished
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Small Length Scale Structure
Modified hard-sphere model Yarusso and Cooper, Macromolecules 1983Spherical ionic aggregates within PS matrix
Hydrated sPS domain
Increasing sulfonation from 22-100% leads to a decrease in the size of the barrier between ionic groups – consistent with improved conductivity.
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Series #1
Series #2
40 Å400 Å
Fluorous domains and
Hydrated sPS domains
Solvent poolsin a
PS matrix
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f Volume fraction of A block (from data)N Interaction between blocks (not known)
Series #1Series #2
Series #1 shows lamellar structureSeries #2 shows phase separation, but no long range order
Compare to diblock copolymer theory Matsen and Bates, Macromolecules 1996
QIm3m
spheresH cylinders
QIa3d
bi-continuous L lamellar
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Conductivity and SANS
(2A)(2B)
(1B)
(1A)
(2C)
(1C)Nafion
Large scale structure is more ordered in Series #1sPS domains are similarLarge scale structure affects the integrity of the membrane, but not the conductivity
1A
2C