Yu. A. Karavanova

Ionic conductivity of hybrid membranes

The recent data obtained by the authors on the conducting properties of certain hybrid membranes have been summarized. To explain the phenomenon of enhancement of ionic conductivity in these systems, the theory of the semielasticity of membrane pore walls has been proposed. It has been shown that in a low humidity region, transport along the surface of incorporated nanoparticles makes an additional contribution to the increment in conductivity.

Diffusion characteristics of mixed-cation ion-exchange membranes

Approaches are proposed for determining diffusion parameters of mixed-cation membranes. One of them is used to evaluate diffusion coefficients and effective ion-exchange constants in membranes containing both H+ and M+ (M = Li, Na, K, Rb) cations from ionic conductance and interdiffusion data for samples in equilibrium with solutions differing in the ratio of salt and acid concentrations.

Diffusion properties of bilayer membranes based on MC-40 and MF-4SC modified with silicon and zirconium oxides

MC-40 membrane samples modified with a thin MF-4SC layer containing inorganic oxide particles have been synthesized. Deposition of an MF-4SC layer raises the diffusion permeability of the membrane. Insertion of ZrO2 or SiO2 nanoparticles into this layer enhances the ion transport selectivity in terms of the cation transport number. The best results are obtained with oxide particles synthesized in the pores of the deposited layer.

Transport properties of asymmetric ion-exchange membranes based on MC-40, MF-4SC, and polyaniline

Asymmetric membrane materials based on MC-40 membranes modified with a thin layer of MF-4SC perfluorinated ion exchangers with introduced polyaniline were obtained. The diffusion parameters of the resulting composites were studied. The anomalous asymmetry of ion transport in neutral solution was found. The diffusion coefficients of individual cations in the membranes with mixed cationic compositions were estimated. The conductivity of the composites was studied. The activation energies were evaluated. It was found that the membranes containing 2% polyaniline exhibited a maximum ionic conductivity, which is consistent with a model of the limited elasticity of membrane pores.

Diffusion characteristics of surface-modified ion-exchange membranes based on MK-40, MF-4SK, and polyaniline

Asymmetric membrane materials based on MK-40 membranes modified with a thin layer of MF-4SK perfluorinated ion-exchange resins with incorporated polyaniline have been studied. The diffusion characteristics of the resulting composites have been analyzed. It has been proved that the membranes with polyaniline undergo a decrease in diffusion permeability, which indicates an increase in selectivity. The modified membranes exhibit a higher cation transport rate. The diffusion coefficients of individual cations in mixed cationic membranes have been estimated. It has been shown that the introduction of small amounts of polyaniline leads to an increase in the proton transport rate.

Diffusion properties of heterogeneous zirconia-doped membranes with the functionalized surface

A study was made of the properties of hybrid materials based on MK-40 heterogeneous membrane, MF-4SK homogeneous membrane, and zirconia with the functionalized surface. The ionic conductivity and diffusion parameters of these materials were investigated. Asymmetry was detected for the diffusion permeability and interdiffusion of HCl and NaCl solutions through the membranes being tested. A consideration was given to the causes of the emergence of the asymmetry and to the mechanisms of the effect of a dopant on the diffusion parameters.

Diffusion characteristics of surface-modified MK-40 mixed-cation ion-exchange membranes

Previously proposed approaches to determining diffusion parameters of mixed-cation membranes have been tested to describe ionic conductance and H+/M+ (M = Li, Na, K) interdiffusion data for asymmetric MK-40-based membranes modified with a thin layer of MF-4SK perfluorinated membrane material containing silica and zirconia additions. The diffusion coefficients, effective ion exchange constants, and asymmetry effects in the membranes are evaluated. The conclusion is made that there is an additional barrier to ion transport across the surface of MK-40 membranes.

Study of ionic conductivity of polytriazole and polynaphthalenediimide ion-exchange membranes

Transport properties of the new polytriazole and polynaphthalenediimide membrane materials have been observed. According to impedance data, the sulfonated polynaphthalenediimide membrane obtained in dimethylsulfoxide demonstrates the maximum value of ionic conductivity. Modification of a membrane material with silica leads to transport properties improvement.

Determination of sulfur-containing anions in alkaline solutions using arrays of DP-sensors based on hybrid perfluorinated membranes with proton-donor dopants

The influence of proton-donor properties and concentration of dopant nanoparticles introduced into Nafion and MF-4SС perfluorosulfonic cation-exchange membranes on the characteristics of cross-sensitive DP-sensors (sensors whose analytical signal is the Donnan potential) in alkaline solutions of sulfur-containing organic compounds were studied. The dopants were acid salts of heteropoly acids (HPAs) and hydrated silica SiO2 and zirconia ZrO2 surface-modified with sulfur-containing groups and an acid HPA salt. A correlation was revealed between the DP-sensor sensitivity to anions (and zwitter-ions) in alkaline solutions, size and proton-donor ability of the added particles, and diffusion permeability of hybrid membranes. Optimum compositions of membranes for arrays of cross-sensitive DP-sensors ensuring the simultaneous determination of cations and anions (and zwitter-ions) in the test solutions with an error of less than 18% were selected.

Synthesis and studies on the diffusion properties of MK-40 cation-exchange membranes modified with ceria

A number of MK-40 cation-exchange membrane samples modified with ceria have been obtained. The membranes have been studied using a set of physicochemical methods, including impedance spectroscopy, scanning electron microscopy, microanalysis, transmission electron microscopy, and XRD phase analysis. It has been shown that the introduction of cerium oxide reduces the humidity content and ionic conductivity of membranes. It is accompanied by a marked increase in the membrane selectivity expressed by a decrease in transfer numbers with respect to anions.