ASAXS characterization of functionalized polyoxadiazoles and polytriazoles

1. Acknowledgements References • D. Gomes, J. Roeder, M.L. Ponce, S.P. Nunes; J. Mem. Sci. 295 (2007) 121–129 • M.L. Ponce, D. Gomes, S.P. Nunes, J. Mem. Sci. submitted • D. Gomes, I. Buder, S. P. J. Polymer Sci., Part B: Polymer Physics 44(16) (2006) 2278-229 • D. Gomes, J. Roeder, M.L. Ponce, S.P. Nunes; J. Power Sources 175 (2008) 49-59 • G. Goerigk, M. L. Ponce, D. Gomes, S. P. Nunes, HASYLAB Jahresbericht 46 (2006) 1183-1184 This work was developed in the frame of the Virtual Institute on Asymmetric Structures for Fuel Cell sponsored by the Helmholtz Association. ASAXS characterization of functionalized polyoxadiazoles and polytriazoles Mariela L. Ponce1, Dominique Gomes1, G. Goerigk2, Suzana P. Nunes1 1Institute of Polymer Research, GKSS Research Centre Geesthacht GmbH, Max-Planck-Str. 1, 21502 Geesthacht2Institute of Solid State Research, Forschungszentrum Jülich, D-52425 JülichE -mail:mariela.ponce@gkss.de Introduction The fuel cell group at GKSS is now investigating sulfonated polyoxadiazoles (SPOD) and polytriazoles (SPT) containing high concentration of basic nitrogen atoms in the repeating unit besides the sulfonic group, which give them many sites for the proton conduction and making them very promising polymeric materials for fuel cells operation at 150-250°C in a low humidity environment. ASAXS was chosen as a convenient method to evaluate the arrangement of sulfonic groups, in order to figure out how their distribution influences the proton transport. Experimental All the polymers used to prepare the membranes were synthesized at GKSS [1-4]; the membrane samples were treated with a RbCl solution to exchange protons by Rb+. The ASAXS measurements were performed at the JUSIFA beamline at DESY-HASYLAB, Hamburg, in the energy range of the K-absorption edge of Rb at 15200 eV. SPT polymer structure POD polymer structure Results The total scattering curves of SPT and SPOD with similar sulfonation degree (Figure 1) show the characteristic broad maximum of the ionomer peak (q = 3.0 nm-1). For both polymers a correlation length of 2.1 nm can be estimated, indicating that the distances between ion clusters are similar. The upturn in intensity at q < 0.1 nm-1 can be attributed to larger inhomogeneities. From the scattering pattern of SPT and POD membranes with different sulfonation level (Fig. 2 and 3), it can be assumed that there is no change in the intercluster distance as a function of the ion content (SPT, q = 3 nm-1; SPOD, q = 3.5 nm-1). Just the change in the relative intensity of the scattering pattern is due to a change in the concentration of aggregate particles. The higher relative intensity at low q for the SPOD12Rx and SPT3Rx, relative to the plain SPOD and SPT polymers, respectively, are attributed to particle aggregation after addition of 5 wt.% of sulfonated silica into the polymer. Similar results have been observed by us when these particles were added to a sulfonated poly(ether ether ketone) matrix [5]. Figure 1. Total scattering curves of SPT and SPOD membranes Figure 3. Total scattering curves of SPOD membranes Figure 2. Total scattering curves of SPT membranes