Structural Studies of Proton-Conducting Fluorous Block Copolymer Membranes

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

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

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

Conductivity and TEM Z. Ken Shi

(2A)(2B)

(1B)

(1A)

(2C)

(1C)Nafion

Conductivity and TEM Z. Ken Shi

(2A)(2B)

(1B)

(1A)

(2C)

(1C)Nafion

1A

1B

1C

2B

2C

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

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

Contrast Variation

Peak #1

Peak #2

Membrane 2B

Peak #1

Membrane 1C

Peak #2

Series #1 – Partially Sulfonated Series #2 – Variable Length

ContrastVariationSeries #1

Peak #1

Peak #2

Binary System

Structure enhanced or diminished

Ternary System

Match core

Match corona

Membrane 1C

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

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 %

Series #2 – Fully sulfonatedContrast Variation

Peak #1

Peak #2

Membrane 2B

Binary System

Structure enhanced or diminished

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.

Series #1

Series #2

40 Å400 Å

Fluorous domains and

Hydrated sPS domains

Solvent poolsin a

PS matrix

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

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