Study of the Internal Morphology of Cation-Exchange Membranes by Means of Electroosmotic Permeability Relaxations

Abstract

The effect of an ac sinusoidal perturbation of known amplitude and frequency superimposed to the usual dc applied electric voltage difference on the electroosmotic flow through three cation-exchange membranes with different morphology has been studied. A dispersion of the electroosmotic permeability on the frequency of the applied ac signal has been found for the three membranes investigated, observing that the electroosmotic permeability reaches maximum values for some characteristic values of the frequency. These characteristic frequency values, which are related to relaxation processes in heterogeneous media, depend on the membrane system and permit to obtain information about the different structures of the membrane system. Thus, the study of the electroosmotic permeability relaxation can be used as a method to study the internal morphology of a cation-exchange membrane in a given electrolyte medium.

Electro-Osmotic Behavior of Polymeric Cation-Exchange Membranes in Ethanol-Water Solutions

“…The images show important morphological differences between the different membrane samples. Heterogeneous membranes can be considered porous membranes, whereas the homogeneous NF117 membrane is considered a dense membrane [ 16 , 17 ]. This perfluorinated membrane is generally assumed to be macroscopically homogeneous, although it has been shown to exhibit certain inhomogeneity in the structure and present microheterogeneity.…”