Ion exchange capacity of Nafion and Nafion composites

Abstract

The ion exchange capacity of recast Nafion films and composites of Nafion and polystyrene microbeads is determined by titration. Composite formation enhances exchange capacity; exchange capacity increases with the surface area of microbeads in the composite. For recast films, an equivalent weight of 996 ± 24 is found, whereas the lowest equivalent weight (highest exchange capacity) found for a composite is 878 ± 8. This suggests that ≳13% of the exchange sites within recast films are inaccessible for ion exchange; for 1100 equivalent weight material, ≳25% of the sulfonates are inaccessible. Equivalent weight results are consistent with an ordered interfacial domain between Nafion and the microbeads. A fractal model based on microbead radii, microbead fraction, and interfacial domain thickness provides a predictive model for designing composites with increased exchange capacity and cation transport.