The coefficients of diffusion permeability of methanol through the synthesized polymer film–sulfonated polystyrene composite membranes and a Nafion-115 membrane are measured. For several composite membranes with significantly different transport properties, the values of the diffusion flux of methanol qdiff through these membranes under the conditions of a direct methanol fuel cell (DMFC) at 60°C and a concentration of the feed solution of 1–2 M are calculated. Direct measurements of the crossover current and methanol crossover qCVA in a DMFC based on these membranes are carried out by cyclic voltammetry (CVA). It is found that the values of qCVA are on average by 15

The structure of multi-walled carbon nanotubes (MWCNTs) is investigated. The MWCNTs were obtained by decomposition of ethylene on a bimetallic Fe-Co catalyst at 670°C. Morphology and structure of the MWCNTs were studied by transmission electron microscope (TEM) JEOL JEM-2100F. The mean diameters of the MWCNTs, the standard deviation, the standard error of the mean (SEM), and the coefficient of variation for the MWCNTs was estimated by the random-secant method in the form of Glagolev–Saltykov point method. The TEM-images of the MWCNTs were analyzed in the program ImageJ.

Novel ion-exchange membranes based on a commercial porous polytetrafluoroethylene film and sulfonated polystyrene are synthesized. To form porous polytetrafluoroethylene–polystyrene composites, thermal polymerization of styrene sorbed in the pores of the matrix-film from the monomer solution is used. The use of porous matrix makes it possible effectively obtaining the composites, used as precursors of the ion-exchange membranes. The sulfonating of the porous polytetrafluoroethylene–polystyrene composites forms the membranes with ion-exchange capacity up to 2.8 mmol/g. The composition and ground physicochemical properties of the new proton-conducting composite membranes are investigated. The developed membranes were shown to have good transport properties. The proton conductivity of water-saturated membranes is as high as 0.13 S/cm at room temperature; the hydration number is 30. Comparative tests of the synthesized membranes and the commercial Nafion-115 membrane in a direct methanol fuel cell at 60°C showed the characteristics of the fuel cell with the developed membranes being at least not inferior to those of a Nafion-115-based cell.

To the article “Influence of Porosity on Fracture Toughness of Hydroxyapatite/Multi-Walled Carbon Nanotubes Biocomposite Materials,” by A. N. Ponomarev, M. S. Barabashko, A. E. Rezvanova, and E. P. Evtushenko, Vol. 63, No. 11, pp. 1885–1890, March, 2021.

Carbon nanomaterials with unique physical and chemical properties find practical applications in various fields, such as in new composite materials, nanoelectronics, medicine, etc. The efficiency of using MWCNTs (multiwalled carbon nanotubes) depends on their morphology, structure, the presence of impurities and defects. In this work, the influence of defects and geometric sizes of CVD MWCNTs on their heat capacity was experimentally studied. The heat capacity of MWCNTs modified by grinding and oxidation with different average outer diameters (7.2 and 18 nm) was measured by the thermal relaxation method in the temperature range from 1.8 to 275 K. The effects of size and dimensionality were found. The character of the temperature dependences of the specific heat of ground and ground-oxidized MWCNTs with various diameters differs fundamentally below approximate to 140 K. The discovered effects are discussed.

The temperature difference between the outer surface and the center of a cylindrical sample of hydroxyapatite (HA) ceramics that arise during annealing/sintering were calculated. HA composites containing small amount of multi-walled carbon nanotubes (MWCNTs) were studied by using the X-ray diffraction methods. It is shown that macrostresses are higher in HA ceramic samples without nanotubes than in samples with MWCNTs. Compressive stresses arise on the outer surface of ceramics and tensile stress arise in the central part during the sintering due to the low thermal diffusivity of HA. This leads to the shifts of the X-ray diffraction peaks. The mechanical properties of HA ceramics with MWCNTs are enchanced due to both high mechanical properties of nanotubes and lower temperature gradients in HA ceramics during heating/cooling in the process of sintering. The additives of MWCNTs also lead to an increase in the density of the HA‒MWCNTs composite. The higher thermal diffusivity of MWCNTs, probably, allows to activate the sintering process in ceramics.

The fracture toughness coefficient K-c of the composite ceramics for medical applications based on hydroxyapatite (HA) with additives of multi-walled carbon nanotubes (MWCNTs) were investigated. Sintering of the composites was carried out at a temperature of 1100 degrees C in an argon atmosphere. The rate of the heating up to temperature of sintering was 20 K/min. HA is a bioactive matrix, and the additives of MWCNTs were used with the purpose of increasing the fracture toughness coefficient K-c. Nanoindentation tests were carried out using microhardness tester Affri DM8 with Vickers pyramid-shaped diamond indenter under a load of 4.9 N. It was found that the additives of MWCNTs with the concentration up to 0.5 wt % lead to a small increase of the K-c of the composite.

DSC and calorimetric studies of multi-walled carbon nanotubes (MWCNTs) with average diameters in the range 7, 9 and 18 nm were carried out. MWCNTs were obtained by the CVD method. The kinetic processes in MWCNTs were studied from room temperature to 550 degrees C in a nitrogen flow using differential scanning calorimetry (DSC) on a Perkin - Elmer - 8000. It was found that exo- and endothermic peaks are not observed on the DSC curves after water evaporation. This indicates that all studied MWCNTs have a small number of defects, functional groups, and other impurities. The heat capacity of MWCNTs was measured by the relaxation method in the temperature range from 2 to 275 K by using PPMS. In the temperature dependences of the specific heat were observed that for MWCNTs with the decrease of the temperature below 20 K the curves shift to lower values with an increase the average diameter. The main result was that at temperatures below 45 K with the decreasing of the nanotubes diameter the ratio of heat capacity of nanotubes to the heat capacity of graphite increases. The perfection of structure and low amount of the defects, functional groups and impurity contamination for MWCNTs were demonstrated in the comparison of the XPS and NEXAFS spectra for these nanotubes with CVD prepared nanotubes (18 nm) after mechanical and chemical functionalization.

Experimental results on the development of two original approaches to obtaining new nanocomposite proton exchange membranes for low-temperature fuel cells are generalized. The first approach consists in in situ modification of the transport channels of commercial proton exchange membranes of the Nafion brand with interpenetrating polymer networks of the introduced polyelectrolyte based on cross-linked polystyrene sulfonate. The second approach is to create a proton exchange nanoscale phase based on polystyrene sulfonate in commercial hydrophobic polymer films. Polystyrene sulfonate is formed during thermal polymerization of styrene sorbed in the films without using ionizing radiation, followed by sulfonation. The influence of the conditions for obtaining membranes on the composition, morphology, transport properties, and results of testing the membranes in low-temperature fuel cells is considered.

Energy spectra of small graphene fragments with and without topological defects (vacancies, nanopores and Stone–Wales defects) are obtained using the Hubbard model based on the approximation of static fluctuations. Modeling of optical absorption spectra is performed for both defect-free and defective small graphene fragments of the lattice. The analysis is given to optical absorption spectra changing with increasing number of vacancies. It is shown how the energy gap depends on the defect configuration and concentration.

The change in the density of electronic states (DOS) near the Fermi level induced by doping, ionic and thermal treatments, is studied. The model of band structure of multi-walled carbon nanotubes (MWCNTs) containing various types of defects, is constructed using experimental data of the DOS near the Fermi level. In the framework of the temperature Green functions method the expression for DOS near the Fermi level is received for MWCNTs of large diameter with impurities and structural defects of short-range order type. The results of theoretical investigations are in a good agreement with the experimental data. The phenomenon of gap opening or closing in the DOS is explained.

Abstract—The thermal polymerization of styrene sorbed from the gas-phase into polymer films of polyvinylidene fluoride (PVDF) is carried out at 110°С. By this method, the “matrix‑polystyrene” composites containing up to 70 wt % polystyrene (PS), which serve as precursors of ion-exchange membranes, are synthesized. Sulfonation of grafted PS produces ion-exchange membranes with the exchange capacitance of 1–2.7 mmol/g and the protonic conductivity reaching 20–200 mS/cm when saturated with water at 25°С. The conductivity values indicate that the nonuniformity of PS distribution over film-matrix cross-section usually encountered when monomer sorbed from the gas phase is polymerized does not exert any noticeable effect on the conduction properties of sulfonated composites. The developed method of preparing composites “polymer matrix‑grafted polystyrene” substantially simplifies the synthesis of the precursor of ion-exchange membranes, decreases the necessary amount of reagents, and considerably enhances the safety of synthesis.

It has been shown that the plane surface of a stressed solid can become morphologically unstable relative to the perturbations of the electron density. The above instability is referred to as dynamic and evolves under the relaxation mechanism determined by the electron-electron interaction. The development of the dynamic instability is accompanied by the formation of a dynamic pattern differing from that which is formed under elastic-diffusion instability. To describe the dynamic pattern, a method has been proposed which takes into account the dynamic displacements of the atoms caused by a change in the interatomic interaction during the electron density redistribution. The origin of the different types of the pattern earlier observed experimentally on the free surface of the stressed solids has been explained. The dynamic displacements of the atoms have been shown to stimulate the diffusion mass transfer resulting in a change of the value and the sign of the diffusion coefficient.

Experimental study of electronic structure of the initial multi-walled carbon nanotubes (MWCNTs) as well as the exposed to annealing and irradiation N-MWCNTs, was carried out by XPS and NEXAFS methods. Based on the obtained photoelectron valence band spectra and C K-edge absorption spectra, a theoretical description of the density of electronic states (DOS) near the Fermi level was proposed to explain the dependence of the DOS and the band gap on temperature, concentration of doping atoms and various atomic configurations formed in a system during synthesis, subsequent ion-beam and heat treatment of MWCNTs.

Calcium phosphate ceramics for medical applications with additives of multi-walled carbon nanotubes were synthesized at a temperature of 1100 °C in the argon atmosphere. The concentration of nanotubes ranged from 0.05 to 0.5 wt.%. The morphology and structure of the powder of multi-walled carbon nanotubes and calcium phosphate ceramics have been characterized by the electron microscope. The most part of the initial nanotubes have distributions of outer diameter 10–25 nm. The multi-walled carbon nanotubes are located in the intergranular space, change their shape and aspect ratio. Diffraction patterns of ceramics show that all samples have apatite structure and any distinct reflections except those of hydroxyapatite are detected. The partial carbonization of ceramics is indicated by the results of FT-IR studies. With an increase of the amount of nanotubes in composite ceramics, the intensity of the carbonate stretching band increases, which may be due to partial oxidation of the nanotubes and as a result leads to more intensive carbonization of the apatite phase. It was found that the mechanical properties of ceramics (compression strength and Vickers microhardness) were improved with the increasing of the amount of nanotubes.

The specific heat of multi-walled carbon nanotubes (MWCNTs) with a low defectiveness and with a low content of inorganic impurities has been measured in the temperature range from 1.8 to 275 K by the thermal relaxation method. The elemental composition and morphology of the MWCNTs were determined using scanning electron microscopy analysis and energy dispersion x-ray spectroscopy. The MWCNTs were prepared by chemical catalytic vapor deposition and have mean diameters from 7 nm up to 18 nm and lengths in some tens of microns. MWCNTs purity is over 99.4 at.%. The mass of the samples ranged from 2–4 mg. It was found that the temperature dependence of the specific heat of the MWCNTs differs significantly from other carbon materials (graphene, bundles of SWCNTs, graphite, diamond) at low temperatures. The specific heat of MWCNTs systematically decreases with increasing diameter of the tubes at low temperatures. The character of the temperature dependence of the specific heat of the MWCNTs with different diameters demonstrates the manifestation of different dimensions from 1D to 3D, depending on the temperature regions. The crossover temperatures are about 6 and 40 K. In the vicinity of these temperatures, a hysteresis is observed.

The experimental data on modification of the surface of metals, alloys and materials coated using the method of irradiation by a heavy-current electron beam with the energy of 300 keV have been given. The specimen surface structure was studied before and after the irradiation using the method of optic microscopy and the surface layer microhardness measurement. The method of electron microscopy was used to analyze the structure and the sizes of dispersed anode material. The films consisting of the crystals with the size of 6 to 8 nm were obtained. The mass transfer processes that occur in the material of metal targets made of Cu, Ti, Mo, Al were studied. The spatial map was compiled for the X-ray field of the plant. The experiments were carried out to define the action of X-ray radiation on the different types of conditionally pathogenic microflora, in particular such bacteria as Escherichia coli, Staphylococcus aureus, and Bacillus subtilis. The fields of application of the plant were defined.