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Large scale structure in perfluorinated ionomer
membranes (Nafion)
L. Rubatat , J.J. Allegraud, G. Gebel , P. van
der Heijden, A. de la Rosa and O. Diat
(odiat_at_cea.fr). CEA-Grenoble, Groupe Polymères
Conducteurs Ioniques, DRFMC/SI3M, 17 av des
Martyrs, 38054 Grenoble cedex 09, France..
Question membrane swelling required an important
structural re-organisation Is it really
thermodynamically possible? What is the relevant
scale to explain the conductivity and the
mechanical properties ? What is the origin for
the anisotropic features in Nafion ?
NAFION ionomer membrane use as proton conductor
with a good chemical and electrochemical
stability, a good mechanical strength, high ion
conductivity.
6ltnlt10 and 100ltmlt1000 equivalent weight from 900
to 1500g/eq.
Membrane characterised by a microphase separation
between ionic domains (inverse micelles) and PTFE
matrix ? ? structural models from Gierke,
Yeager, Dreyfus, Gebel
NAFION structure from Å up to micron
Zoom and Debye-Bueche fit of the low-q part on
the Nafion SAXS curve
Large Swelling Ionomer peak and saxs knee
position vs. f
x
d f-0.5 for flt60 typical for rod-like
aggregates similar dilution process at two
different scales
Large aggregates or correlation in orientation
of the elongated polymeric aggregates?
Description using Debye-Bueche analysis
At large volume fraction - deviation of the
rod-like dilution law Power law close to
-1 Suggestion of ribbon-like aggregates collapsed
in a lamellar packing
Correlation function
g(r)e -r/x
For fp16
Elongated aggregates observed by AFM tapping
mode. (solution deposit on silicon wafer)
Form factor of polymeric cylindrical core-shell
vs contrast variation
Polymeric cylinder with ø 20Å, Lgt500Å
AFM studies in a non-contact mode
NAFION dynamics from Å up to micron
Anisotropy under stretching?
Amplitude and phase AFM image of the stretched
film
mSAXS studies (ESRF-ID1, ID18f3) on stretched
membrane
QNES with Mibemol spectrometer (LLB)
Field cycling NMR Relaxometry
SAXS/WAXS experiment on ID2
Birefringence analysis microscopic observation
biaxial model to quantify transmission
variation vs stertching
Model Powder of Bundle of cylindrical aggregate
to analyse ionomer peak position as a function
stretching azymuthal distribution
The intensity of the dispersion curves is related
to S/V. 2 types of dynamics with a change around
l9 (l nb of water molecules per charge)
Correlation scattering anisotropy and
birefringence
Short and long range diffusion
Correlation static - dynamic in Nafion
1st hydration mechaanism hydration of charge
surface around the polymeric aggregates water
swelling (water on water)
2nd hydration mechanism Propose the existence of
collapsed region. - hydration of charge surface
by opening collapsed region
Summary Prospectives

• Recent publications L. Rubatat et al,
  Macromolecules 35(10), (2002) 4050-4055 AL
  Rollet et al, J. Phys. Chem. B 106(12), (2002)
  3033-3036. O. Diat et al, Physica B (2004) P.
  van der Heijden et al, Macromolecules, 37 (2004)
  5327-5337 J. of Polym. Sci. Part B Polymer
  Physics , 42 (2004) 2857-2870. L. Rubatat et al,
  Macromolecules (2004) accepted.
• Acknowledgement to local contact persons T.
  Narayan, P. Panine, V. Urban, I. Grillo, M.
  Müller and S. Roth and CEA technical support JJ.
  Allegraud, G. Albert

• Elongated aggregates (ratio 100).
• Anisotropy induced by strain.
• Large scale organisation.
• Origin of the large scale nodules - contributions
  on the macroscopic protonic conductivity?
• Ionic distribution in these nodules with respect
  to the polymer matrix?
• control of the orientation of the elongated
  aggregates with an external field.