Nanostructure of Nafion membrane material as a function of mechanical load studied by SAXS

The nanostructure of a perfluorinated membrane material (Nation 117 by DuPont) is investigated as a function of strain and load by small-angle X-ray scattering (SAXS) at a synchrotron source. Two-dimensional SAXS patterns are evaluated utilizing the multi-dimensional chord distribution function (CDF). Anisotropy of the extruded material is considered. Both the ionomer domain and matrix polymer nanostructure are studied. For the neat material the classical ionomer domain model (domains as inverted micellae interconnected by channels) is confirmed and refined. Matching the plastic deformation behavior of the material, the domain structure in the relaxed and in the elongated state are found to be very similar. During elongation, ionomer channels open to form hollow ionomer layers('slits') that are oriented parallel to the strain with a thickness of 1.9 nm and a long period of 3.8 nm. The slit height increases from 3 nm at elongation epsilon = 0.5 to 6 nm at epsilon = 1.25, whereas the slit width decreases to 1.5 nm. The ultimate structure is characterized by ensembles of not more than three slits that are in good lateral register. In the polymer matrix during elongation, cylindrical crystallites with a thickness of 2.5 nm and a most probable height of 7 nm are disrupted and parallelized with respect to the straining direction. The ultimate structure before sample failure is characterized by a broad domain height distribution ranging from a most probable domain height of 4 nm with a corresponding ultimate inclination of 40degrees to some perfectly parallelized domains of 20 nm height. (C) 2003 Elsevier Science Ltd. All rights reserved.