Characterization of MK-40 Membrane Modified by Layers of Cation Exchange and Anion Exchange Polyelectrolytes

Abstract

Coating of ion exchange membranes used in electrodialysis with layers of polyelectrolytes is a proven approach that allows for the increasing of the limiting current, the suppressing of sedimentation, the controlling of the intensity of generation of H+ and OH− ions, and also the improving of monovalent selectivity. However, in the case when two materials with the opposite sign of the charge of fixed groups come in contact, a bipolar boundary is created that can cause undesirable changes in the membrane properties. In this work, we used a MK-40 heterogeneous membrane on the surface of which a layer of polyethyleneimine was applied by adsorption from a solution as a model of heterogeneous membranes modified with oppositely charged polyelectrolyte. It was found that, on one hand, the properties of modified membrane were beneficial for electrodialysis, its limiting current did not decrease and the membrane even acquired a barrier to non-selective electrolyte transport. At the same time, the generation of H+ and OH− ions of low intensity arose, even in underlimiting current modes. It was also shown that despite the presence of a layer of polyethyleneimine, the surface charge of the modified membrane remained negative, which we associate with low protonation of polyethyleneimine at neutral pH.

Transport and Electrochemical Characteristics of CJMCED Homogeneous Cation Exchange Membranes in Sodium Chloride, Calcium Chloride, and Sodium Sulfate Solutions

“…However, in the case of the CMX membrane ( Figure 3 d–f), drying occurs fairly evenly over the surface and it is not possible to visualize the “rapid water evaporation” spots, although these membranes contain reinforcing fabric as well. Apparently, this is due to the fact that both the reinforcing cloth and the inert filler of the CMX ion-exchange composite material are made of the same PVC polymer, that is, they have good adhesion [ 44 , 70 ].…”

Selectivity of Transport Processes in Ion-Exchange Membranes: Relationship with the Structure and Methods for Its Improvement

“…There is another effective way to improve the selectivity of membranes by coating layers with fixed groups of opposite charge. For example, the surface of cation exchange membranes can be modified with polyethyleneimine [ 295 , 296 , 297 , 298 , 299 ] or polyaniline [ 234 , 300 , 301 , 302 , 303 ]. It should be noted that such membranes also differ in the asymmetry of ion transport and, in particular, in diffusion permeability [ 304 ].…”

Polyethylenimine-Modified MK-40 Membranes: Estimating the Electrical Conductivity and Generation of H+ and OH− Ions from Potential Transients

“…Earlier, the current-voltage curves for the considered membranes were registered using the same unit, and these data were used to determine the experimental limiting current densities. These current-voltage profiles were discussed in detail in our previous study [16]. We note that current-voltage curves registered before and after measuring a set of potential transients were identical, suggesting the possibility that the coatings were stable, at least during short-term use; however, we carried out neither long-term investigations of the membranes' electrochemical properties, nor did we perform a comparative analysis of the membrane's surface composition before and after the current was applied.…”