Hierarchical structure analysis of graft-type polymer electrolyte membranes consisting of cross-linked polytetrafluoroethylene by small-angle scattering in a wide- range

Iwase, Hiroki*; Sawada, Shinichi; Yamaki, Tetsuya; Koizumi, Satoshi; Onuma, Masato*; Maekawa, Yasunari

Fundamental understanding of the structure-property relationship of polymer electrolyte membranes (PEM) is prerequisite for a material design satisfying PEM performance requirement. Small-angle scattering in a wide- range was observed by focusing small-angle neutron scattering (FSANS), small-angle neutron scattering (SANS), and small-angle X-ray scattering (SAXS). The hierarchical structure of the PEM was characterized as being composed of conducting layers (graft domains) in lamellar stacks with 48-57 nm spacing on the surfaces of 480 nm diameter crystallites and ultra-small structures with a 1.7 nm correlation distance of the sulfonic acid groups in the conducting layers. From the change in the SAXS profiles as a function of grafting degrees, it was revealed that the graft domains around the crystallites were connected with the adjoining domains and thus, the PEMs with a higher degree of grafting had conductivity higher than that of Nafion.