Structure and transport properties in sulfonated polyimide membranes (sPI)

1. Used Sequence : Focalised x-ray beam using a mirror ( 40 m) or a refractive lens D Conical glass capillary t d z Evolution equation : xy translation stage y • At the sample position : • beam size  2 - 20 m • flux 1010 ph/s @ 13 keV CCD + intensifier camera Swelling effect Microbeam and small angle x ray scattering (SAXS) on ID13 beamline at the ESRF (+ID18) q=4p/l sin(q/2) with q the scattering angle Conclusions: Isotropic structure in plane only. Scattering peak at larger angles, more intense in the plane of the membrane (3 orders, d  15Å). Ionomer peak (d  200Å) : position depends on the block size. Usaxs upturn more intense in the thickness than in plane. Anisotropy from molecular to micron scale Anisotropic swelling (between the plan and the thickness) Large domains of water - SEM Observation after stretching and rupture : (The samples are stretched till the rupture, at cte velocity in then swelling state and then lyophilised) highlight of a “skin” - TEM Observation : Samples are embedded in a resin. Very thin slices (100nm) obtained using an ultramicrotom membrane CEI=1.26, x=5 membrane CEI=1.26, x=7 Structure and transport properties in sulfonated polyimide membranes (sPI) Olivier Diat, Jean-François Blachot, Anne-Laure Rollet, Laurent Rubatat, Gilles Mercier et Gérard GebelDépartement de Recherche Fondamentale sur la Matière Condensée, SI3M, Groupe Polymères Conducteurs Ioniques, CEA-Grenoble, 17 rue des martyrs, 38054 Grenoble cedex 9 Sulfonated polyimide = ionic conducting polymer for electro-chemical applications like electrodialysis or fuel cell H2/O2 ionomer membranes are usually characterised by nano-phase separation between ionic domains and the polymer matrix. Compared to Nafion, the ionomer peak, characteristic of the ionic domains distribution is located at smaller scattering angles.  domains 5 times larger Block copolymer : 1<X<10 et 5<Y<20 equivalent weight from 400 up to 1000 g/eq Membrane swelling mainly along the thickness  structural anisotropy Question:At what relevant scale ? Influence on the transport properties ? X-ray (SAXS) or neutron (SANS) small angle scattering is a suitable technique to study the structure of ionomer membranes from nanometers up to micron scale. Membranes are investigated at different swelling ratios from dry to water immersed regime. (humidity controlled cell) The microbeam camera permits to probe the membrane along its thickness direction. plane thickness Transport properties studies Microscopic studies - Optical microscopy : Ionic conductivity measurements using impedence spectrometry: Rigid polymer (naphtalenic) compared with avec flexible sPI (pthalic) On side On surface Polymer X=5 et Y=12 Flexible polymer : percolation threshold Rigid polymer : anisotropic structure 100 µm 250 µm Birefringent membrane in thickness. Two entangled phases. Diffusion coefficient determined using Gradient Pulsed field NMR technique: Rigid polymer (naphtalenic) Diffusion coefficient are 4 times larger in the plane Increasing the IEC and the copolymer block size the system appear less homogeneous. Conclusions & Perspectives • anisotropy of the structure from molecular to micrometer scale. • anisotropy of the transport properties • Two phases in coexistence (a dense one with oriented polymer chains and an amorphous one) favoured by the long block sequences. • Entanglement and lamellar organisation of both phases. • AFM impedencemetry studies controlling the humidity rate. • Orientation of the domains under external field (in progress) • Casting process studies (in progress) • Water molecules location - infrared spectroscopy (in progress) • Lifetime studies in operating mode (thesis in progress) Acknowledgements : ESRF, ILL, LLB, CERMAV, CGRM for help and access to instruments MRT financial support ( PREDIT and Réseau technologique PACo) Collaboration: -internal with A.Guillermo, M.Pinéri, Y. Maréchal et P. Capron ; external with IEM-Montpellier (G. Pourcelly), Ecole polytechnique (P. levitz), LMOPS (R. Mercier), ESRF (N. Galatanu), CRMD-Orléans (P.Porion) • References : - Ionomers : characterization, theory and applications Schlick, S., Ed. ; CRC Press: Boca Raton, 1996 • - Cornet, N.; Diat, O.; Gebel, G.; Jousse, F.; Marsacq, D.; Mercier, R.; Pineri, M. • J. New Mat. for Electrochem. Syst. 2000, 3, 33-42 • - J.F. Blachot, O. Diat, J. L. Putaux, A.L. Rollet, L.R. Rubatat, C.Valois, M. Müller and G. Gebel • Accepted in J. New Mater. Electrochem. Syst. (2002).