1. Effect of water and ethanol on the size distribution
of free-volume holes in Nafion membrane
J. Čížek, Z. Barnovská, M. Šourek, I. Procházka
Faculty of Mathematics and Physics, Charles University Prague, Czech Republic

2. Introduction
Nafion
Nafion – perfluorinated polymeric sulfonic acid developed by du Pont Nemours

3. Introduction
Nafion
Nafion – perfluorinated polymeric sulfonic acids developed by du Pont Nemours
proton conductivity, no electron conductivity
membrane for fuel cells
excellent temperature and mechanical stability
resistent to chemical decomposition

4. Introduction
Nafion
Nafion – perfluorinated polymeric sulfonic acids developed by du Pont Nemours
hydrophobic PTFE backbone
hydrophilic ionic clusters nm
P.J. Brookman, J.W. Nicholsonin: Developments in Ionic Polymers, vol. 2,
eds. A. D. Wilson and H. J. Prosser (Elsevier Applied Science Publishers: London, 1986)

5. Experimental
influence of water and ethanol on free volumes in Nafion membrane
Nafion membrane N-1110 (Du Pont), surface density 500 g m-2, EW = 1100 g
thickness mm
samples for positron annihilation: multi-stack consisting of 4 membranes
22Na spot 1.5 MBq
mylar foil 2 mm
Nafion N1110

6. LT spectroscopy Digital LT spectrometer:
F. Bečvář et al., Nucl. Instr. Meth. A 539, 372 (2005)
 BaF2 scintilators truncated cone ( mm, thickness 12 mm)
 Two photomultipliers Hamamatsu H3378
input
detector 2
AS BUS
External
trigger
data
transfer
to PC
detector 1
 two 8-bit digitizers Acqiris DC211, sampling rate 4 GHz
 time resolution 145 ps (FWHM 22Na)
 measurement at RT + in-situ investigations at elevated temperatures

7. Decompositon of LT spectra
LT code version 9 (J. Kansy, University of Silesia, Katowice )
e+ annihilation  discrete exponential components
Ps annihilation  complex component
log-normal distribution of annihilation rates
due to varying size of free volume holes
Tao - Eldrup model  radius R of free volume holes

8. As received Nafion N1110 – positron lifetime results
Nafion N1110 – as received state
e+ annihilation:
t1 = 205(9) ps, I1 = 5.2(8) %
t2 = 430(3) ps, I2 = 80(1) %
free e+
trapped e+
Ps annihilation:
tp-Ps = 130(5) ps, Ip-Ps = 3.7(4) %
to-Ps = 3.10(3) ns, Io-Ps = 11.1(4) %, so-Ps = 1.06(6) ns
para – Positronium (p-Ps)
ortho – Positronium (o-Ps)
dispersion
mean value of distribution

9. Water content in as-received Nafion N1110
as-received Nafion N1110 – drying at 130oC
drying kinetics – two processes:
relative weight loss:
– fast: t1 = 1.0 ± 0.4 min
– slow: t2 = 8 ± 2 min
water content in as-received Nafion: (6.7 ± 0.8) wt.%
t (min) 20 40 60 80
100
relative weight loss (%) 2 4 6 8

10. Dried Nafion N1110 – positron lifetime results
Nafion N1110 – as received state
dried state (130oC, 2h)
e+ annihilation:
t1 = 205(9) ps, I1 = 5.2(8) %
t1 = 204(8) ps, I1 = 6.0(5) %
t2 = 430(3) ps, I2 = 80(1) %
t2 = 442(5) ps, I2 = 80.1(4) %
Ps annihilation:
p-Ps
tp-Ps = 130(5) ps, Ip-Ps = 3.7(4) %
tp-Ps = 130(6) ps, Ip-Ps = 3.5(4) %
to-Ps = 3.10(3) ns, Io-Ps = 11.1(4) %,
so-Ps = 1.06(6) ns
to-Ps = 3.09(2) ns, Io-Ps = 10.5(4) %,
so-Ps = 1.00(3) ns
o-Ps
No significant change of positron parameters

11. Water uptake into Nafion N1110
T = 25oC
t (min) 20 40 60
weight increase (%) 10 30

12. Water uptake into Nafion N1110
T = 25oC
T = 30oC
t (min) 20 40 60 10 30
weight increase (%)

13. Water uptake into Nafion N1110
T = 25oC
T = 30oC
T = 40oC 40 30
weight increase (%) 20 10 20 40 60
t (min)

14. Water uptake into Nafion N1110
T = 25oC
T = 30oC
T = 40oC
T = 60oC
t (min) 20 40 60 10 30
weight increase (%)

15. Water uptake into Nafion N1110
T = 25oC
T = 30oC
T = 40oC
T = 60oC
T = 80oC
t (min) 20 40 60 10 30
weight increase (%)

16. Water uptake into Nafion N1110
T = 25oC
two processes:
relative weight increase:
T = 30oC
T = 40oC
T = 60oC
slow
T = 80oC
T = 100oC
very fast
t (min) 20 40 60 10 30
weight increase (%)

17. Water uptake into Nafion N1110
absorption kinetics – two processes:
very fast process
slow process
characteristic time t2  min
T ( o C) 20 40 60 80
100
120
t2 (min)
characteristic time t1 = (11 ± 1) s
filling of ionic clusters with water
expansion of ionic clusters into free volumes
T ( o C) 20 40 60 80
100
120
t1 (s) 4 6 8 10 12 14 16 18 22

18. Water uptake into Nafion N1110 - PAS
positron components
boiled in
water 2 h
boiling in water 2 h  both fast & slow process
influence of water on free volumes in Nafion
water content (wt.%) 10 20 30 40 50
lifetime (ps)
150
200
250
300
350
400
450
500 t1 t2
volume expansion  increase of t1, t2
boiled in
water 30 s
boiling in water 30 s  very fast process only
water content (wt.%) 10 20 30 40 50
Intensity (%) 60 80
100 I1 I2

19. Water uptake into Nafion N1110 - PAS
o-Ps component
water content (wt.%) 10 20 30 40 50
to-Ps (ns)
2.75
2.80
2.85
2.90
2.95
3.00
3.05
3.10
3.15
lifetime
influence of water on free volumes in Nafion
boiled in
water 30 s
boiled in
water 2 h
to-Ps decreases
so-Ps firstly increases and then decreases
water content (wt.%) 10 20 30 40 50
so-Ps (ns)
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
dispersion
boiled in
water 30 s
water 2 h
IPs increases
water content (wt.%) 10 20 30 40 50
IPs (%) 12 14 16 18 22
intensity
boiled in
water 30 s
water 2 h

20. Water uptake into Nafion N1100 - PAS
influence of water on distribution of free volumes
as-received
1.8
1.6
1.4
1.2
H (R) * IPs
1.0
0.8
0.6
0.4
0.2
0.0
0.0
0.2
0.4
0.6
0.8
1.0
R (nm)

21. Water uptake into Nafion N1110 - PAS
influence of water on distribution of free volumes
dried at 130oC / 2h
as-received
1.8
1.6
1.4
1.2
H (R) * IPs
1.0
0.8
0.6
0.4
0.2
0.0
0.0
0.2
0.4
0.6
0.8
1.0
R (nm)

22. Water uptake into Nafion N1110 - PAS
influence of water on distribution of free volumes
ionic clusters filled with water
& incomplete splitting of free volumes
boiled in water 30s
dried at 130oC / 2h
as-received
R (nm)
0.0
0.2
0.4
0.6
0.8
1.0
H (R) * IPs
1.2
1.4
1.6
1.8

23. Water uptake into Nafion N1110 - PAS
influence of water on distribution of free volumes
boiled in water 2h
splitting completed
boiled in water 30s
narrow distribution of free volumes
dried at 130oC / 2h
as-received
R (nm)
0.0
0.2
0.4
0.6
0.8
1.0
H (R) * IPs
1.2
1.4
1.6
1.8

24. Water uptake into Nafion N1110 - PAS
o-Ps component
to-Ps decreases
water content (wt.%) 10 20 30 40 50
to-Ps (ns)
2.75
2.80
2.85
2.90
2.95
3.00
3.05
3.10
3.15
boiled in
water 2 h
water 30 s
lifetime
influence of water on free volumes in Nafion
so-Ps firstly increases and then decreases
water content (wt.%) 10 20 30 40 50
so-Ps (ns)
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
dispersion
boiled in
water 30 s
water 2 h
IPs increases
water content (wt.%) 10 20 30 40 50
IPs (%) 12 14 16 18 22
intensity
boiled in
water 30 s
water 2 h
water absorption in ionic clusters:
volume expansion
splitting of free volumes

25. Water uptake into Nafion N1110 - PAS
o-Ps component
water content (wt.%) 10 20 30 40 50
to-Ps (ns)
2.75
2.80
2.85
2.90
2.95
3.00
3.05
3.10
3.15
lifetime
influence of water on free volumes in Nafion
boiled in
water 30 s
boiled in
water 2 h
water content (wt.%) 10 20 30 40 50
so-Ps (ns)
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
dispersion
boiled in
water 30 s
water 2 h
very fast process
water content (wt.%) 10 20 30 40 50
IPs (%) 12 14 16 18 22
intensity
boiled in
water 30 s
water 2 h

26. Water uptake into Nafion N1110 - PAS
o-Ps component
water content (wt.%) 10 20 30 40 50
to-Ps (ns)
2.75
2.80
2.85
2.90
2.95
3.00
3.05
3.10
3.15
lifetime
influence of water on free volumes in Nafion
boiled in
water 30 s
boiled in
water 2 h
water content (wt.%) 10 20 30 40 50
so-Ps (ns)
0.7
0.8
0.9
1.0
1.1
1.2
1.3
1.4
dispersion
boiled in
water 30 s
water 2 h
slow process
water content (wt.%) 10 20 30 40 50
IPs (%) 12 14 16 18 22
intensity
boiled in
water 30 s
water 2 h

27. Water uptake into Nafion N1110 - PAS
mean free volume Vmean
Nafion-N1110
210
200
190
180
Vmean (Å3)
170
160
150
140 10 20 30 40 50
water content (%)

28. Water uptake into Nafion N1110 - PAS
fast process: Vmean decreases due to expansion of ionic clusters & splitting of holes
broad distribution of free volumes
Nafion-N1110
210
200
190
180
Vmean (Å3)
170
160
150
140 10 20 30 40 50
water content (%)

29. Water uptake into Nafion N1110 - PAS
slow process: splitting completed  most of free volumes are split
narrow distribution of free volumes
Nafion-N1110
210
200
190
180
Vmean (Å3)
170
160
150
140 10 20 30 40 50
water content (%)

30. Water uptake into Nafion N1110 - PAS
mean free volume
Nafion-N117, H.S. Sodaye et al. J. Polymer Sci. B 35, 771 (1997)
Nafion-N1110
water content (%) 10 20 30 40 50
Vmean (Å3)
140
150
160
170
180
190
200
210

31. Ethanol uptake into Nafion N1110
weight increase
t (min) 10 20 30 40 50 60
relative weight increase (%)
100
200
300
400
500
600
T = 25oC

32. Ethanol uptake into Nafion N1110
weight increase
t (min) 10 20 30 40 50 60
100
200
300
400
500
600
T = 35oC
T = 25oC
relative weight increase (%)

33. Ethanol uptake into Nafion N1110
weight increase
t (min) 10 20 30 40 50 60
100
200
300
400
500
600
T = 40oC
T = 35oC
T = 25oC
relative weight increase (%)

34. Ethanol uptake into Nafion N1110
weight increase
t (min) 10 20 30 40 50 60
100
200
300
400
500
600
T = 50oC
T = 40oC
T = 35oC
T = 25oC
relative weight increase (%)

35. Ethanol uptake into Nafion N1110
weight increase
t (min) 10 20 30 40 50 60
100
200
300
400
500
600
T = 60oC
T = 50oC
T = 40oC
T = 35oC
T = 25oC
relative weight increase (%)

36. Ethanol uptake into Nafion N1110
weight increase
t (min) 10 20 30 40 50 60
100
200
300
400
500
600
T = 70oC
T = 60oC
T = 50oC
T = 40oC
T = 35oC
T = 25oC
relative weight increase (%)

37. Ethanol uptake into Nafion N1110
weight increase
t (min) 10 20 30 40 50 60
100
200
300
400
500
600
T = 78oC
T = 70oC
T = 60oC
T = 50oC
T = 40oC
T = 35oC
T = 25oC
relative weight increase (%)

38. Ethanol uptake into Nafion N1110
weight increase
t (min) 10 20 30 40 50 60
100
200
300
400
500
600
T = 78oC
T = 70oC
T = 60oC
T = 50oC
T = 40oC
T = 35oC
T = 25oC
relative weight increase (%)
relative weight increase:

39. Ethanol & water uptake into Nafion N1110
comparison of water and ethanol absorption in Nafion N 1110 at room temperature
t (min) 10 20 30 40 50 60
relative weight increase (%) 80
100
120
140
160
ethanol
water

40. Ethanol uptake into Nafion N1110
relative weight increase:
absorption kinetics – two processes:
fast process
T ( o C) 20 40 60 80
100
120 2 4 6 8 10 12 14 16 18
t2 (min)
slow process
characteristic time t2  10 t1
penetration of ethanol into PTFE parts
characteristic time t1 < 1.5 min
absorption of ethanol in ionic clusters
both processes  substantial increase of rate at elevated temperatures
T ( o C) 20 40 60 80
100
120
t1 (min)
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8

41. Ethanol uptake into Nafion N1110
absorption kinetics – two processes:
fast process
slow process
characteristic time t1 < 1.5 min
characteristic time t2  10 t1
absorption of ethanol in ionic clusters
penetration of ethanol into PTFE parts
both processes  substantial increase of rate at elevated temperatures
relative weight increase:
T ( o C) 20 40 60 80
100
120
relative contribution
0.0
0.2
0.4
0.6
0.8
1.0
slow process, x2
relative contributions:
fast process, x1

42. Ethanol uptake into Nafion N1110 - PAS
distribution of free volumes H(R)
decrease of the mean radius of free volume holes
increase in concentration of free volume holes
2.5
as-received
dried 135 o
C / 2h
2.0
T = 25 o
C in ethanol
T = 40 o
C in ethanol
T = 60 o
C in ethanol
1.5
H (R) * IPs
1.0
0.5
0.0
0.2
0.3
0.4
0.5
0.6
0.7
R (nm)

43. Ethanol & water uptake into Nafion N1110 - PAS
distribution of free volumes H(R)
comparison of water and ethanol influence on distribution of free volume holes
water absorption  smaller size & lower concentration of free volume holes
R (nm)
0.2
0.3
0.4
0.5
0.6
0.7
0.0
1.0
1.5
2.0
2.5
as-received
dried 135 o
C / 2h
T = 60
C in ethanol
T = 100
C in water
H (R) * IPs

44. Kinetics of ethanol uptake – intensity of o-Ps component
in-situ positron lifetime measurement of Nafion N1110 immersed in ethanol
T = 21oC
t (h) 10 20 30 40 50 60 70 80 90
100
110
120
130
140
150
160
IPs (%) 15 25 -4 -2 2 4
residuals (s)
T = 25oC
T = 25oC

45. Kinetics of ethanol uptake – intensity of o-Ps component
in-situ positron lifetime measurement of Nafion N1110 immersed in ethanol
T = 42oC
T = 21oC
t (h) 10 20 30 40 50 60 70 80 90
100
110
120
130
140
150
160 15 25 -4 -2 2 4 6
IPs (%)
residuals (s)
T = 40oC
T = 25oC
T = 40oC
T = 25oC

46. T = 60oC T = 40oC T = 25oC T = 60oC T = 60oC T = 40oC T = 42oC
t (h) 10 20 30 40 50 60 70 80 90
100
110
120
130
140
150
160 14 16 18 22 24 26 28 32 34 -4 -2 2 4 6
IPs (%)
residuals (s)
T = 60oC
T = 40oC
T = 25oC
T = 60oC
T = 40oC
T = 25oC

47. Kinetics of ethanol uptake – PAS
two processes:
slow process ( 70 %)
splitting of free volumes due to expansion
of ionic clusters & penetration into PTFE part
T = 42oC
T = 21oC
T = 60oC
t (h) 10 20 30 40 50 60 70 80 90
100
110
120
130
140
150
160 14 16 18 22 24 26 28 32 34
IPs (%)
T = 25oC
T = 40oC

48. Kinetics of ethanol uptake – PAS
two processes:
slow process ( 70 %)
at elevated temperatures (T  40oC)
t2 comparable with that of weight increase
splitting of free volumes due to expansion
of ionic clusters & penetration into PTFE part
T ( o C) 20 40 60 80
100
120
t2 (min) 50
150
200
PAS
weight measurement

49. Kinetics of ethanol uptake – PAS
two processes:
very slow process ( 30 %)
slow process ( 70 %)
t3  25 – 30 h
splitting of free volumes due to expansion
of ionic clusters & penetration into PTFE part
further redistribution of free
volumes
T = 42oC
T = 21oC
T = 60oC
t (h) 10 20 30 40 50 60 70 80 90
100
110
120
130
140
150
160 14 16 18 22 24 26 28 32 34
IPs (%)
T = 25oC
T = 40oC

50. Conclusions
Nafion N1110
water concentration in as-received state: (6.7 ± 0.8) wt.%
water absorption: up to 40 wt.%
ethanol absorption: up to 500 wt.%
water & ethanol up-take occurs by two processes (fast & slow)
effect of absorbed water & ethanol on free volume holes
- increase in concentration of free volume holes
- decrease in the mean size of free volume holes
expansion of ionic clusters  splitting of free volumes

51. Ethanol uptake into Nafion N1110 - PAS
in-situ positron lifetime measurement
intensity of Ps component
ethanol uptake
T = 60oC 35
ethanol uptake
T = 40oC
drying
T = 25oC 30
ethanol uptake
T = 25oC 25
drying
T = 40oC
IPs (%) 20 15
virgin T = 25oC 10
100
200
300
400
500
t (h)

52. As-received Nafion N1110 – positron lifetime results
scaled size distribution of free volumes – comparison of PTFE and Nafion
compared to PTFE, Nafion exhibits lower concentration and sharper size
distribution of free volume holes
PTFE (teflon)
ionic clusters
R (nm)
0.0
0.2
0.4
0.6
0.8
1.0
H (R) * IPs
1.2
1.4
1.6
1.8
Nafion, as-received

53. Ethanol uptake into Nafion N1110 - PAS
mean free volume Vmean
ethanol content (wt. %)
100
200
300
400
Vmean (Å3)
190
195
205
210
215
T = 40oC