![Page 1: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/1.jpg)
Nafion: Hydration, Microstructure and Schroeder’s paradox
Viatcheslav Freger
Maria Bass , Amir Berman (BGU)Oleg Konovalov, Amarjeet Singh (ESRF)
Technion – Israel Institute of TechnologyWolfson Department of Chemical Engineering
Haifa, Israel
![Page 2: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/2.jpg)
Nafion and Its Uses
Fuel Cells
Membrane electrolysisSensors
Catalysis
An ionomer developed by DuPont in 70s
![Page 3: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/3.jpg)
Unique Microstructure: Microphase separation and 2D Micelle Morphology
Schmidt-Rohr and Chen, Nat Mater., 2008
Gebel, Diat et al, Macromolecules, 2002, 2004
Gebel, Polymer, 2000
Hsu and Gierke, JMS, 1983
![Page 4: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/4.jpg)
2D Morphology: Transport vs. Hydration
Conductivity
VF et al., JMS, 1999Kreuer, JMS, 2001
0.001
0.01
0.1
1
0.01 0.1 1
water volume fraction XVD/
Dw
Blum et al.SPEPEEKKNafion
3D
2D
Water self-diffusion (NMR)
![Page 5: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/5.jpg)
Schroeder’s Paradox: Two Isotherms?
Bass and Freger, 2008
0
10
20
30
0 0.2 0.4 0.6 0.8 1
water activity
l
vapor
liquid
Li-Nafion
Sample SampleOsmotic stressor
solution
![Page 6: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/6.jpg)
Schroeder’s Paradox and Water Transport
If the thermodynamic potential of water is ill-defined, how
does one model water transport and “water management”?
51~
Hw
www J
RT
CDJ
![Page 7: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/7.jpg)
Schroeder’s paradox explained?
Choi and Datta (JES, 2003) were first to publish an explanation,
but they assumed
permanent pores;
hydrophobic pore walls (despite ionic groups);stability of surface structure and 3-phase line.
![Page 8: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/8.jpg)
Fixing the Model: Structure and Equilibrium
Four terms are the minimal set
osmotic “inflation” interface “corona”
20( ) ( ) /o eff g G BR
1
34
5
2
)( ge vv
R
VF, Polymer, 2003; JPC B, 2009
Minimize g = f – lto getl
![Page 9: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/9.jpg)
Chemical Equilibrium as Balance of Pressures
2
2/3
(1 )s
out sin d
RR R
g
”’
l”l’
Pressures:out , in - osmoticd - inflation (transient)s - interfacial-elastic (“Laplace”)
VF, JPC B, 2009
The interfacial tension is zero, but the “Laplace” pressure is not unless = 1.
![Page 10: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/10.jpg)
Surface Equilibrium
Two more equilibrium conditions at the surface:
Balance of 3 tensions (Neumann construction)
Equilibrium between polymer bulk and surface
vapor
matrix (2)
an ionic group
liquid (1)12
12a b
c d e
VF, JPC B,2009
![Page 11: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/11.jpg)
Surface Equilibrium: Interim Summary
In vapor water gets buried under surface; s ≥ 0.
In liquid micelles are inverted and s = 0 (Schroeder’s paradox).
Nafion should dissolve in water, but dissolution never happens (relaxation time ≥ 105 s).
However, (quasi-)dissolution may occur at the surface.
2)1( Rs
normal-type micelles(“spaghetti”)surface-aligned
bundle (“macaroni”)
water
![Page 12: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/12.jpg)
Examining the Surface Structure: GISAXS
keV 8for 2.0 c
nm 3~pd
Rubatat and Diat, Macrmolecules, 2007
(bulk SANS)
![Page 13: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/13.jpg)
ESRF and ID10B
![Page 14: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/14.jpg)
Nafion Surface in Vapor (GISAXS)
0.001
0.01
0.1
1
0.01 0.1 1 10Qxy , A-1
Qxy
*I,
A-1
a.u.
0.110.170.20.25
100 nm thick Nafion film spin-cast on a Si waferT = 30 C, RH ~ 97%Beam 8 keV
Bass et al., JPC B, 2010
![Page 15: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/15.jpg)
GISAXS: Going Under Water
water vapor
C18-capped Si substrate
Nafion film
![Page 16: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/16.jpg)
Vapor vs. Liquid: Contact Angle and AFM
CA: Nafion surface is hydrophobic in vapor and hydrophilic in water
AFM: under water the surface gets rougher (surface tension drops).
Dry = 96.4 ± 1.2hydrophobic
Vapor RH=97% = 94.5 ± 1.1hydrophobic
water
Air bubble
Water drop
Air Water drop
Air
Liquid water = 25.4 ± 0.25
hydrophilic
![Page 17: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/17.jpg)
Hydrophilic vs. Hydrophobic Substrate
OTS on Si: = -59 mV, = 130o (Yang & Abbott, Langmuir, 2010)
Dura et al., Macromolecules, 2009 (NR)
C18-capped Si substrate
Nafion film
Native Si substrate (SiO2)
Nafion film
![Page 18: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/18.jpg)
Micelle Orientation at Interfaces
C18-capped Si substrate
a micelle bundle
Vapor
Native Si (SiO2) substrate
Water
Nafion film Micellebundles
bundlesbreaking up
Bass et al., 2010
Some of these are metastable non-equilibrium structures! (non-relaxed elastic stress, relaxation time >105 s)
Balsara et al, NanoLett, 2007
![Page 19: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/19.jpg)
Summary
2)1( Rs
Vapor Nafion Liquid
Solid Nafion is a non-equilibrium structure.
Non-relaxed pressures in Nafion result in a non-thermodynamic behavior (Schroeder’s paradox); this needs to be accounted for in transport modeling.
Interfaces affect the morphology and orientation of micelles in thin Nafion films; this could be attractive for developing barriers with enhanced and stable transport characteristics.
![Page 20: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/20.jpg)
ISFESRF
Maria Bass
Oleg Konovalov, Amarjeet Singh, Jiři Novak (ESRF, ID10B)
Amir Berman, Yair Kaufman, Juergen Jopp (BGU)
Special thanks: Emmanuel Korngold (BGU), Klaus-Dieter Kreuer, Martin Ise (MPI Stuttgart)
Thanks
![Page 21: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/21.jpg)
Another old puzzle: microscopic vs. macroscopic swelling
The relative change of Bragg spacing (d-do)/d (“microscopic swelling”) may be compared with the relative macroscopic linear expansion (1/p – 1)1/3 calculated from l.
Though for high l the relation is as for dilute 2D micelles, for solid Nafion (small and moderate l) it is nearly linear, as if the structure is 1D (lamellae)
Gebel, 2000; Fujimura et al., 1981, 1982
![Page 22: Nafion : Hydration, Microstructure and Schroeder’s paradox Viatcheslav Freger Maria Bass, Amir Berman (BGU) Oleg Konovalov, Amarjeet Singh (ESRF) Technion](https://reader035.vdocument.in/reader035/viewer/2022062421/56649e175503460f94b02c09/html5/thumbnails/22.jpg)
Microscopic vs. macroscopic swelling
The model shows a good agreement with scattering data, provided a 2D morphology is “plugged in”
0
1
2
3
4
5
6
0 0.5 1 1.5
Linear expansion
Mic
rosc
opic
sw
ellin
g
D=3
D=2
D=2 var
1
10
100
0.01 0.1 1
p
dm
ax, n
m
constantvariable
1
10
0
23
11 11
n for D=2 theoretical initial slope is 7 (exp 6)
n D
gDp w
g g
d dn
d D D