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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.

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This paper describes the development of a novel pressure-driven nanofluidic-flowing liquid junction (NFLJ) reference electrode with an invariant liquid junction potential, for use in potentiometric sensors. These NFLJ reference electrodes have been shown to have a stable and reproducible potential with electrolyte flow under 5 ml per year. Use of the NFLJ reference electrode will result in sensors with outstanding precision that are maintenance free for periods of one year or more. This research is based on an innovative combination of nanochannel glass (NCG) and the nanofluidic liquid junction structure. The typical NCG array used for NFLJ reference electrodes has fewer than 200 channels with IDs smaller than 500 nm. Sensors using the NFLJ reference electrode demonstrate better potential stability, faster response time, and longer operational life than conventional commercial gel filled reference electrodes and are competitive with laboratory quartz fiber electrodes.