Abstract
The hydration in liquid water of various thermally treated SPEEK membranes was determined and confronted with data in saturated water vapor. Significant differences, which correspond to the so-called Schröder paradox, are observed only in un-crosslinked ionomers with IEC>2eq/kg.After cation exchange in electrolyte solutions (2 and 0.1mol/L), the hydration and density of the ionomers was determined and confronted with a physical model. There is no clear correlation with cation properties, such as ionic radius or Robinson–Stokes hydration numbers.The ionic conductivity ranges from 3mS/cm for K, NH4 and Mg-exchanged membranes to 0.6mS/cm for Ca and Zn. Although the latter might be related to ionic cross-linking by the divalent cations, the relatively high conductivity of Mg ions might be useful for electrochemical applications.
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