Permselectivity and microstructure of anion exchange membranes

The water content, the ion exchange capacity, the transport number of counter-ion of the AMV and AMX anion exchange membranes were determined. The two-phase model (gel phase and interstitial phase) of structure microheterogeneity was validated by means of conductivity measurements. The chronopotentiometric results allowed us to affirm the overall surface homogeneity of the membranes. According to the two-phase model, the influence of the gel phase and the interstitial phase on the membrane permselectivity was discussed in detail. Majorities of co-ions exist in the interstitial phase, thus they have no influence on the transport of counter-ions in the gel phase. The determination of the KCl amount sorbed in the interstitial phase confirmed the existence of partition equilibrium between the interstitial phase and the external solution. Such partition equilibrium can be considered within the microheterogeneous model in order to represent the internal structure of the electromembranes.

On the microstructural scale, the AMV and AMX homogeneous anion exchange membranes are described as two-phase systems: gel phase and interstitial phase with the volume fractions f1f1 and f2f2, respectively. Increase in the volume of interstitial phase leads to a higher amount of KCl electrolyte found in the interstitial solution. Equilibrium partition between the external solution and the interstitial solution can be considered within the microheterogeneous model in order to represent the internal structure of the electro-membranes.Figure optionsDownload as PowerPoint slide