Structural anisotropy and transport properties in sulfonated polyimide membranes [Anisotropie structurale et des propriétés de transport dans les membranes en polyimide sulfoné]
Résumé
Anisotropic structure and transport properties were studied in sulfonated polyimide membranes using small-angle X-ray microscattering (microSAXS), pulse-field-gradient nuclear magnetic resonance (NMR) and scanning electron microscopy (SEM). Based on the MicroSAXS data, the in-plane structure appears to be isotropic while a significant anisotropy is observed along the thickness dimension. This result was confirmed by mechanical deformation experiments: SEM images of stretched and fractured specimens revealed a layered structure. The evolution of the ionic conductivity as a function of the ion content suggests the presence of anisotropic domains. The NMR determination of diffusion coefficients along the planar and thickness directions revealed a significant anisotropy, which confirmed the structure-transport relationships.