I. V. Falina

Electrotransport properties and morphology of MF-4SK membranes after surface modification with polyaniline

The method of template synthesis is used for the surface modification of MF-4SK membranes with polyaniline. The influence of the time of polyaniline synthesis in the surface layer of a perfluorinated MF-4SK membrane on its morphology and electrotransport properties is investigated. It is established that under the synthesis conditions, a gradient distribution of polyaniline develops across the thickness of the membrane, and as a result of this, an anisotropic composite structure is formed. It is shown that the specific electrical conductivity and the electroosmotic and diffusion permeability exhibit an extremal character as functions of the time of polyaniline synthesis. When the orientation of these composite membranes is changed with respect to electrolyte flow, an asymmetry effect in their diffusion characteristics is found. With the application of the bilayer fine porous membrane model, the modified-layer thickness is estimated, and the determining influence of the difference in absolute values of effective fixed-charge volume densities on the development of the asymmetry effect is found.

Influence of conditions of polyaniline synthesis in perfluorinated membrane on electrotransport properties and surface morphology of composites

The conductivity, diffusion, and electroosmotic permeability of composites, obtained in different conditions of polyaniline synthesis on the surface or in volume of perfluorinated MF-4SK membrane, were studied. The oxidative polymerization of aniline was carried out in static conditions in mixture of monomer and oxidant solutions, in concentration field by method of successive diffusion of polymerization solutions through the membrane in water, and in an external electrical field. The concentration of polymerization solutions, the type of electron acceptors, duration of synthesis, and current density were varied to obtain a set of composites. The certain advantages of every method of polyaniline chemical template synthesis were revealed to prepare the materials with required set of the electrotransport characteristics.

New approach to the characterization of ion-exchange membranes using a set of model parameters

An extended three-wire model of the conductivity of ion-exchange membranes is proposed. The model includes a set of three-wire model equations supplemented with coupling equations between three-wire model parameters and the parameters of a microheterogeneous model. To calculate the complete set of parameters for evaluating the structural inhomogeneity of a membrane and calculating its effective electrotransport properties, it is necessary and sufficient to get only the concentration dependence of the specific conductivity of the membrane, which simplifies the characterization procedure. The model was verified based on independent experimental data and the calculations of transport-structural parameters with the use of the microheterogeneous model. It was found that the proposed model approach makes it possible to obtain a reliable combination of structural parameters to characterize the volume fractions of conductive phases and their mutual arrangement in the ion exchange material peculiar to the membrane test sample.

Epoxy-Polyelectrolite Composites as a Basis of Intellectual Coating for Protection from Underfilm Corrosion on Cathodically Polarizable Structures

In this paper substantiated the possibility of creating on the basis of epoxy-polyelectrolyte composites of anticorrosive coatings sensitive to corrosive environment and its application for protection from underfilm corrosion cathode-polarized structures, which include, for example, underground steel pipelines.

Effects of mixed conductivity of nanocomposite membranes MF-4SC/PANI

Changes in the conducting and hydrophilic properties of composites MF-4SC/polyaniline (PAni) under conditions of prolonged synthesis have been studied. A maximum of PAni content of about 0.20 by weight, which can be incorporated into the matrix of MF-4SC under these conditions of synthesis, is determined. Percolation behavior of electrical conductivity of the composites after drying was observed. The conductivity of PAni salt inside MF-4SC was estimated within the frames of the percolation model. Using the fibrous cluster model of the membrane and the conductivity data on individual PAni, theoretical assessment of the electrical conductivity of nanocomposite MF-4SC/PAni has been performed. Reasons for a significant reduction in the conductivity of PAni during its integration into the structure of the initial matrix were discussed. A scale of membrane conductivity, reflecting changes in the electrical conductivity of composites at various stages of synthesis, was drawn.

Theoretical estimation of differential coefficients of ion-exchange membrane diffusion permeability

It has been shown that the differential coefficients of the diffusion permeability of MK-40 and Nafion 425 sulfonic cation-exchange membranes to solutions of diverse electrolytes can be calculated within the framework of the theory of generalized conductivity of structurally inhomogeneous membranes with the use of model transport-structural parameters. The calculation has been performed on the basis of experimentally measured concentration dependences of the specific electrical conductivities and diffusion fluxes of electrolytes through membranes into water. The results of the model calculation are in satisfactory agreement with the data obtained by an independent method without resorting to notions of the structural organization of a membrane.

Model description of conductivity of ion–exchange membranes in a wide range of concentrations of electrolyte solution

The possibility of applying the exponential and power equations of Lichtenecker for theoretical estimation of conductivity of ion–exchange membranes in a wide range of concentrations of equilibrium solutions is discussed on the basis of the experimentally obtained concentration dependences of conductivity for different types of ion–exchange membranes of Russian and foreign origin. It is shown that model parameters determined on the basis of experimental data on membrane conductivity obtained in the range of dilute solutions or any other concentration range according to the specific options of the measurement technique can be used to calculate conductivity of membranes in concentrated solutions.

Transport Asymmetry of Novel Bi-Layer Hybrid Perfluorinated Membranes on the Base of MF-4SC Modified by Halloysite Nanotubes with Platinum

Three types of bi-layer hybrid nanocomposites on the base of perfluorinated cation-exchange membrane MF-4SC (Russian analogue of Nafion®-117) were synthesized and characterized. It was found that two membranes possess the noticeable asymmetry of the current–voltage curve (CVC) under changing their orientation towards the applied electric field, despite the absence of asymmetry of diffusion permeability. These phenomena were explained in the frame of the “fine-porous model” expanded for bi-layer membranes. A special procedure to calculate the real values of the diffusion layers thickness and the limiting current density was proposed. Due to asymmetry effects of the current voltage curves of bi-layer hybrid membranes on the base of MF-4SC, halloysite nanotubes and platinum nanoparticles, it is prospective to assemble membrane switches (membrane relays or diodes) with predictable transport properties, founded upon the theory developed here.

Influence of inert components on the formation of conducting channels in ion-exchange membranes

In this work, the results of investigation of the influence of inert binder and reinforcing fabric on structural organization and mechanism of current transfer in homogeneous and heterogeneous ion-exchange membranes are presented by theoretical analysis of parameters of the extended three-wire conductivity model. It was established that analogy in reorganization of the current paths takes place in the course of inclusion of the reinforcing fabric in perfluorinated membranes and addition of polyethylene and nylon 6 to ion-exchange resins during preparation of heterogeneous membranes. In comparison with perfluorinated membranes, the essential difference in conducting properties of heterogeneous membranes is the opportunity for the current transfer via the channel filled with equilibrium solution. The size of this channel decreases with increase in the volume fraction of the inert component inside the membrane.

Effect of counter- and co-ions on the structural transport parameters of sulfoacid cationite membranes

The diffusion permeability and specific electroconductivity of MK-40 sulfoacid cationite and Nafion 425 membranes are studied experimentally in NaOH, NaCl, and HCl solutions with various concentrations. The resulting concentration dependences of the electrodiffusion characteristics and data on the nonexchange sorption of the electrolytes are used to calculate the structural transport parameters of the membranes in terms of a two-phase conduction model. Analysis of a set of parameters, including the electroconductivity and diffusion permeability of the membrane gel phase, the volume fractions of the conductive phases, and a parameter that reflects their relative positions, the Donnan constant, and the diffusion coefficients of counter and co-ions in the membrane gel phase reveals the effect the nature of counter- and co-ions has on the electrodiffusion, structural, and sorption characteristics of sulfoacid cationite membranes with different types of structure.