Insight into the multiscale structure of pre-stretched recast Nafion® membranes: Focus on the crystallinity features

•Extended structural analysis (SAXS and WAXD) of pre-stretched recast Nafion membranes.•SAXS exhibited different behaviors of the ionomer and matrix peaks upon stretching.•WAXD showed that the crystallites strongly align along the stretching direction.•SAXS evidenced reduced effect of stretching at mesoscopic scale.•WAXD evidenced strong effect of stretching at molecular scale.

The structure of solution cast Nafion® membranes that were uniaxially stretched, and then thermally annealed was studied over an extended observation window, from a few angstroms to several hundreds of angstroms, using both Small-Angle X-Ray Scattering (SAXS) and Wide-Angle X-Ray Diffraction (WAXD). This Nafion® membrane preparation allowed highlighting new structural features, never reported previously. Indeed, while SAXS data evidenced moderate effect of stretching with different behaviors of the matrix and ionomer peaks, WAXD spectra showed a strong stretching induced anisotropy of the crystalline phase. These results defy the Nafion® structural models and call for further theoretical and experimental developments taking into account these new data.

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