The modern concepts on the origin of electroconvection (EC) are surveyed briefly and the known mechanisms of this phenomenon are classified. Factors that influence the EC character and intensity at...

Ion-exchange membranes (IEMs) find more and more applications; the success of an application depends on the properties of the membranes selected for its realization. For the first time, the results of a comprehensive characterization of the transport properties of IEMs from three manufactures (Astom, Japan; Shchekinoazot, Russia; and Fujifilm, The Netherlands) are reported. Our own and literature data are presented and analyzed using the microheterogeneous model. Homogeneous Neosepta AMX and CMX (Astom), heterogeneous MA-41 and MK-40 (Shchekinoazot), and AEM Type-I, AEM Type-II, AEM Type-X, as well as CEM Type-I, CEM Type-II, and CEM Type-X produced by the electrospinning method (Fujifim) were studied. The concentration dependencies of the conductivity, diffusion permeability, as well as the real and apparent ion transport numbers in these membranes were measured. The counterion transport number characterizing the membrane permselectivity increases in the following order: CEM Type-I ≅ MA-41 < AEM Type-I < MK-40 < CMX ≅ CEM Type-II ≅ CEM Type-X ≅ AEM Type-II < AMX < AEM Type-X. It is shown that the properties of the AEM Type-I and CEM Type-I membranes are close to those of the heterogeneous MA-41 and MK-40 membranes, while the properties of Fujifilm Type-II and Type-X membranes are close to those of the homogeneous AMX and CMX membranes. This difference is related to the fact that the Type-I membranes have a relatively high parameter f₂, the volume fraction of the electroneutral solution filling the intergel spaces. This high value is apparently due to the open-ended pores, formed by the reinforcing fabric filaments of the Type-I membranes, which protrude above the surface of these membranes.

Artificial charged membranes, similar to the biological membranes, are self-assembled nanostructured materials constructed from macromolecules. The mutual interactions of parts of macromolecules leads to phase separation and appearance of microheterogeneities within the membrane bulk. On the other hand, these interactions also cause spontaneous microheterogeneity on the membrane surface, to which macroheterogeneous structures can be added at the stage of membrane fabrication. Membrane bulk and surface heterogeneity affect essentially the properties and membrane performance in the applications in the field of separation (water desalination, salt concentration, food processing and other), energy production (fuel cells, reverse electrodialysis), chlorine-alkaline electrolysis, medicine and other. We review the models describing ion transport in ion-exchange membranes and electromembrane systems with an emphasis on the role of micro- and macroheterogeneities in and on the membranes. Irreversible thermodynamics approach, “solution-diffusion” and “pore-flow” models, the multiphase models built within the effective-medium approach are examined as the tools for describing ion transport in the membranes. 2D and 3D models involving or not convective transport in electrodialysis cells are presented and analysed. Some examples are given when specially designed surface heterogeneity on the membrane surface results in enhancement of ion transport in intensive current electrodialysis.