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内容記述 |
We comprehensively investigate the hierarchical structures of the previously reported radiation-grafted anion-exchange membranes (AEMs), consisting of p-(2-imidazoliumyl) styrene graft-polymers onto poly(ethylene-co-tetrafluoloethylene) (ETFE) films with different grafting degree (GD), using the partial scattering function (PSF) analysis. We first confirm the existence of a characteristic GD (GDc) of 20?25%, over which AEMs show enhanced anion transport efficiency. To clarify the structure features in correlation with GDc, two AEMs with GD of 14% and 42% (AEM14 and AEM42) are selected for PSF analysis, where AEMs are treated as a 3-component system, containing EFTE base polymer (BP), graft polymer (GP) and water (W). Our results reveal the two different microphase inversions across GDc in tens of nanometer and a few nanometer ranges, respectively. In the large scale (> 10 nm), at GD < GDc (i.e., AEM14), the hydrophilic GP/W domains and dry GP domains coexist together, which are spherically shaped with an average radius of ~11.5 nm, dispersing in the BP matrix. While at GD > GDc (i.e., AEM42), a network structure is formed by irregularly shaped BP domains with a radius of gyration of ~9.5 nm dispersing in GP/W matrix (hydrophilic/hydrophobic phase-inversion compared to AEM14). In small scale (< 10 nm) ion-channel inversion from water-in-polymer to polymer-in-water in hydrophilic region is confirmed by the bicontinuous local structures shown in AEM14 and AEM42 with GP or W being the rich phase, respectively. The extraction of these unique structure factors enables the prediction of scattering intensity profiles of AEMs with GD > 42%. |
