The degree of swelling of the lithium form of the perfluorosulfonic acid membrane Nafion in alcohols (ethanol, 2-propanol), water-alcohol mixtures, and highly polar aprotic solvents (N,N-dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP)) was studied, as well as the thermodynamics of membrane-solvent interaction using microcalorimetry. It was shown that the equilibrium swelling degree of the membrane correlates with the donor number of the solvent and the enthalpy of polymer swelling. The enthalpy of membrane swelling in all studied solvents is negative, indicating polymer solvation. Concentration dependences of the swelling and mixing enthalpies in DMF and NMP were studied in greater detail. The negative values of the swelling enthalpy across the entire concentration range of the solvents indicate good thermodynamic compatibility of the membrane with the solvent and highlight the advantage of using these solvents to produce Nafion dispersions due to their strong solvating properties.

Методами изотермической сорбции и микрокалориметрии исследована термодинамика взаимодействия полиперфторсульфоновой кислоты Nafion с водой. Определены концентрационные зависимости энергетических и энтропийных параметров смешения водных растворов Nafion и показано, что энергия Гиббса и энтальпия смешения отрицательны, а энтропия смешения положительна во всем диапазоне составов раствора. Экспериментальные изотермы сорбции воды и концентрационные зависимости энтальпии разбавления водных растворов проанализированы с использованием термодинамической модели, учитывающей парные невалентные взаимодействия в растворе, неравновесную стеклообразную структуру полимера и эффекты диссоциации ионогенных сульфогрупп Nafion. Расчетное значение параметра Флори–Хаггинса составило 1.48, а значение его энтальпийной компоненты близко к нулю.

— Nickel nanoparticles are obtained by electrical explosion of wire under the action of a high-voltage discharge followed by condensation in an inert gas medium. When butane is added to the gas medium, a carbon shell is deposited onto the condensing nickel particles. Immediately after the synthesis, liquid-phase modification of nanoparticles is carried out with aqueous solutions of polysaccharides agarose and gellan. As a result, a polymer shell is formed on particles of Ni and nickel particles coated with a carbon shell (Ni@C). The dispersity, crystalline structure, and magnetic properties of Ni and Ni@C nanoparticles are characterized by transmission microscopy, X-ray diffraction analysis, and vibration magnetometry. The total carbon content on the surface of the nanoparticles is determined by thermal analysis with simultaneous mass spectrometry. It is shown that, under the studied conditions, polysaccharides are deposited onto the nanoparticles in amounts up to 2 wt % to form a shell with a thickness of about 4 nm. When agarose is used as a modifier, the content of the polysaccharide increases with the concentration of the modifying solution. When gellan is used as a modifier, a more complex concentration dependence is observed: an initial increase is followed by a decrease in the amount of deposited polysaccharide. The results are discussed from the viewpoint of the influence of the molecular weight of a polymer on the adsorption process.

The synthesis of carbon-encapsulated copper nanoparticles (Cu & C NPs) by the high-productive method of the electrical explosion of wire (EEW) is presented. Copper wire was evaporated by high-energy electrical current pulses. Evaporation of Cu and the consequent condensation of spherical nanoparticles took place in argon with the controlled addition of butane, which provided encapsulation of copper nanoparticles in carbon shells. Carbon was deposited in the form of several graphite layers, which completely covered the surface. The encapsulation diminished the agglomeration of carbon-encapsulated copper nanoparticles (Cu@C NPs) during their condensation and substantially diminished their average diameter. Upon the deposition of about 4 % of carbon, the average diameter of nanoparticles decreased more than three-fold - from 130 to about 40 nm. Simultaneously, the specific surface area of Cu@C NPs increased from 7 to 35 m2/g. The deposited dense and gas tight carbon shells protected the surface of particles from oxidation. It prevented the self-ignition of as-synthesized nanoparticles at the exposure to ambient air and provided stability to oxidation during long-term storage as well.

Magnetic and structural properties iron oxide micro- and nanoparticles and composites based on epoxy resin at different mass concentrations of particles are investigated (0, 5, 10, 30%). Commercial Alfa Aesar microparticles and nanoparticles obtained by electric explosion of wire with different dispersion parameters were compared. Magnetoimpedance detection of stray magnetic fields of the obtained composites in the form of cylinders using a strip multilayer film element [FeNi/Cu]5/Cu/[FeNi/Cu]5 was carried out. It is shown that it is possible to determine the position of filled magnetic composites at different mass concentrations of magnetic micro- or nanoparticles with different parameters of dispersion of the ensemble using magnetoimpedance detection. Ключевые с

The peculiarities of structure and static magnetic properties of composites based on epoxy resins with microparticles of iron oxide FeOx, which are used as model materials for magnetic detection, have been investigated. The [FeNi/Cu]5/[Cu/[Cu/FeNi]5 film element with transverse magnetic anisotropy is used as a sensing element of the prototype of detector of weak magnetic fields operating on the basis of the magnetoimpedance (MI) effect. It is shown that there is a linear dependence of the specific magnetization on the concentration of microparticles in the range of 0–70 wt

The thermodynamics of interaction between poly(perfluorosulfonic acid) Nafion and water is studied by isothermal sorption and microcalorimetry. The concentration dependences of energy and entropy parameters of mixing of Nafion aqueous solutions are determined. It is shown that the Gibbs energy and the enthalpy of mixing are negative while the entropy of mixing is positive over the entire range of solution compositions. The experimental water sorption isotherms and the concentration dependences of the enthalpy of dilution of aqueous solutions are analyzed in terms of the thermodynamic model allowing for pair nonvalence interactions in solution, nonequilibrium glassy structure of the polymer, and effects of the dissociation of ionic sulfo groups of Nafion. The calculated value of the Flory–Huggins parameter is 1.48, and the value of its enthalpy component is close to zero.

Ferrogels based on polyacrylamide with embedded magnetic particles of strontium hexaferrite SrFe12O19 with their content up to 17.9 wt % have been synthesized and studied. The enthalpy of adhesion of polyacrylamide to the surface of particles is determined by the calorimetric method using a thermochemical cycle. Its negative values indicate good adhesion. This leads to a significant decrease in the degree of swelling of ferrogels with increasing particle content. The modulus of elasticity of ferrogels is measured under uniaxial compression with and without an external uniform magnetic field of 27.5 mT. The effect of a uniform magnetic field of 420 mT on the magnetostriction of ferrogels has been studied. It has been shown that ferrogels based on polyacrylamide filled with strontium hexaferrite underwent universal stretching in a magnetic field, leading to an increase in their volume and additional swelling.

Theoretical model has been developed for the diffusion-limited photocatalytic degradation of organic dye in aqueous solution by composite hydrogel filament with embedded photocatalyst nanoparticles. The model included transition of dye molecules from the supernatant solution into the composite hydrogel, diffusion of the dye inside and pseudo first-order reaction of dye photocatalytic degradation. Theoretical model was verified by the experimental studies of the methyl orange dye photocatalytic degradation in aqueous solution by composite polyacrylamide hydrogel different degrees of crosslinking with embedded commercial TiO2 nanoparticles Degussa/Evonik P25. The integral rate of the dye concentration diminishing of the supernatant solution can be nicely fitted by a single exponential decay function with an apparent kinetic constant of dye photocatalytic degradation reaction. The dependence of the apparent kinetic reaction constant, the diffusion coefficient of dye through hydrogel and the value of the "true" kinetic reaction constant has been discussed. (C) 2021 Elsevier Inc. All rights reserved.

Results of experimental study of a heat production by systems of magnetite particles, immobilized in an epoxy composite and placed under the action of oscillating magnetic fields are presented. The samples, consisting of the particles with diameters 8.3, 16 and 180 nm were studied and the specific loss power (SLP) per 1 g of magnetic particles was evaluated as a function of their volume fraction in an epoxy composite, the frequency and the intensity (H $$_{0})$$ of the applied magnetic field. It was shown that SLP increased with the volume fraction of magnetic particles in the composite due to the dipole–dipole interaction in concentrated magnetic dispersions. Unexpectedly, intensities of the heat productions in the composites with embedded batches of particles 16 and 180 nm in diameter were practically the same; the thermal effect increased with the applied field amplitude faster than $$\hbox {H}_{0}^{2}$$ .

Objective : to evaluate the features of reparative chondrogenesis and osteogenesis in animal experiments with the implantation of porous poly(2-hydroxyethyl methacrylate) (pHEMA) hydrogel into osteochondral defects. Materials and methods . Cylindrical pHEMA implants (5 mm in diameter) were synthesized by radical polymerization. The implants were subjected to light microscopy and mechanical tests to characterize the structure and viscoelastic properties of the material. In experimental group #1, four pHEMA specimens were implanted into formed defects in the distal femoral epiphysis of rabbits. In experimental group #2, allogeneic chondrocytes were applied to the surface of four specimens before implantation. In the control series, four defects were not replaced with implants. Tissue regeneration was investigated by morphological and morphometric methods 30 days after operation. Results . The pHEMA implants were heterogeneous specimens with irregularly shaped pores – up to 30 × 10 μm at the surface and 300 × 120 μm inside. With >10% static compressive stress, the Young’s modulus was 54.7 kPa. For dynamic stress, increased frequency of compression-relaxation cycles from 0.01 Hz to 20.0 Hz led to increased storage modulus from 20 kPa to 38 kPa on average, and increased loss modulus from 2 kPa to 10 kPa. Indicators of semi-quantitative assessment of local inflammatory response to pHEMA implantation had the following values in points: pHEMA, 4.7 ± 0.3; pHEMA with allogeneic chondrocytes, 6.0 ± 1.0; control, 4.3 ± 0.3. The ratio of connective, bone, and cartilage tissues proper in the regenerates had the following respective values: pHEMA, 79%, 20%, 1%; pHEMA with chondrocytes, 82%, 16%, 2%; control, 9%, 74%, 17%. Conclusion . In a short-term experiment, pHEMA implants did not trigger a pronounced inflammatory response in the surrounding tissues and can be classified as biocompatible materials. However, the tested implants had low conductivity with respect to bone and cartilage cells, which can be improved by stabilizing the pore size and increasing the rigidity when synthesizing the material.

Kinetics of magnetostriction of ferrogel with physical networking based on natural polysaccharide guar gum with embedded strontium hexaferrite magnetic particles were studied in the uniform magnetic field 420 mT. An ellipsoidal sample was elongated by 37% along the applied field and contracted by 15% in the transverse direction, while its volume was kept constant. The characteristic time of magnetostriction was 440 s. Dynamic mechanical analysis in an oscillatory mode showed that the deformation of ferrogel is mostly elastic rather than viscous. Its storage modulus was almost constant in a frequency range of 0.1–100 Hz and by at least an order of magnitude larger than the loss modulus. Meanwhile, a developed theoretical model based on the elasto-viscous behaviour of the ferrogel failed to estimate correctly the experimental value of its magnetostriction. Calculated values of the elongation of ferrogel in the field were several orders of magnitude lower than those observed in the experiment for the ferrogel with physical networking. Consistency between the experiment and the theory was achieved using the alternative consideration based on the deformation of a liquid droplet of ferrofluid. The applicability of such an approach was discussed concerning structural relaxation properties of the ferrogel with physical networking.This article is part of the theme issue ‘Transport phenomena in complex systems (part 1)’.

Zero-valent metallic iron nanoparticles (NPs) with modified surface were embedded in poly(isoprene) (PI) and the enthalpy of interfacial adhesion in resulted ferroelastomers was evaluated. Iron NPs were synthesized by the method of electrical explosion of wire (EEW) in inert gas. Modification of their surface was performed by the in situ liquid treatment of the active condensed NPs in the EEW installation. The enthalpy of mixing of poly(isoprene) with Fe NPs was determined using thermochemical cycle based on the isothermal calorimetry measurement of the enthalpy of dissolution of PI/Fe composites in chloroform at 25 degrees C. Using these values the enthalpy of adhesion of PI to the surface of modified Fe NPs was evaluated using Langmuir-type isotherm. It was shown that the enthalpy of adhesion strongly depends on the properties of the surface of Fe NPs and its modification. It was the lowest in the case of oxidized Fe NPs and the highest for Fe NPs which surface was modified by pre-deposited polymeric shells.

The possibilities of producing large batches of magnetic nanoparticles (MNPs) using electrical explocion of the wire (EEW), laser target evaporation, and spark discharge are considered. MNP bioapplications require production of magnetic materials in the form of as stabilized aqueous suspensions or hydrogels with magnetic fillers; therefore, some details of synthesis of these materials and their certification are discussed. The problems of the interaction of MNPs with biological systems, biocompatibility, the applicability of ferrogel substrata to cellular technology and regenerative medicine, and as biomimetics in the development of magnetic biosensors are considered. The results of analysis of some biological experiments with various suspensions prepared based on the same MNP batch are presented. An analysis of the examples of magnetic biodetection and existing theoretical approaches will allow estimation of prospects of this scientific direction to develop highly sensitive film sensors based on the giant magnetic impedance effect for biomedical applications.

The enthalpy, Gibbs free energy, and entropy of mixing of polyacrylamide with agarose have been determined using thermodynamic cycles based on microcalorimetry and isothermal equilibrium sorption data. The enthalpies of solution in water have been measured, and water sorption isotherms have been obtained for films of polyacrylamide, agarose, and their mixtures in different ratios. The sorption data have been processed used a sorption model that takes into account the effect of polysaccharide chain stiffness on the change in the chemical potential of water upon the formation of a solution during sorption. The model relationships are shown to be in good agreement with the experimental isotherms over the entire range of variation of the polymer volume fraction and the relative vapor pressure. It has been found that the enthalpy of mixing of polyacrylamide and agarose is negative over the entire range of compositions. Mixtures containing less than 50 wt % agarose are thermodynamically incompatible and are characterized by a positive Gibbs energy of mixing, whereas Gibbs energies are negative for mixtures containing more than 50% agarose. The calculated values of the entropy of mixing are negative in the entire range of agarose to polyacrylamide ratios, thereby indicating ordering in this polymer mixture. The results of studying the thermodynamic compatibility of polyacrylamide and agarose are compared with the swelling behavior and mechanical properties of hydrogels based on semi-interpenetrating networks of these polymers.

Polyelectrolyte gels and ferrogels (FG) are attracting special interest in biomedicine. Here we describe our experience developing functional magnetic ferrogels for regenerative medicine and magnetoimpedance biosensing for measuring stray fields of nanoparticles in FG with a multilayered sensitive element. We discuss the possibility of developing a new generation of drug delivery systems for magnetic field assisted delivery, positioning and biosensing.

The regularities of the formation of the structural state and the piezoelectric properties of PVDF films with a thickness of about 170 nm, obtained by spin-coating on glass substrates, are studied. Using the methods of IR spectroscopy, X-ray diffraction, and Raman spectroscopy, the dependences of the ratio of crystalline alpha and beta-phases on the initial acceleration and maximum substrate rotation speed are established. The optimal values of these parameters are found that provide the maximum concentration of the beta phase (similar to 60 %) with spontaneous electric polarization. It was shown that in the films studied, the value of the piezoelectric coefficient d(33), determined by the method of piezoresponse force microscopy, can take anomalously large values (up to 74 pm/V). This is due to the fixing effect of the glass substrate, which provides significant residual deformation of the polymer films.

Biomedical engineering is the most promising field for the application of ferrogels as scaffolds for cell culturing in regenerative medicine, targeted drug delivery, and biosensorics. This study is focused on the contribution of ferric-oxide magnetic nanoparticles (MNPs) to the biocompatibility of ferrogels with human dermal fibroblasts. The results of experiments with polyacrylamide gels filled with MNPs are presented. These experiments demonstrate that, regardless of the mechanical and electrical characteristics of ferrogels, MNPs have a significant effect on the biological activity of cells.

Important experimental data were obtained for the development of an integrated technology for the destruction of accumulated volumes of environmentally hazardous technical mixtures of polychlorobiphenyls. The proposed technology for the destruction of ecotoxicants includes a chemical and subsequent pyrolytic stages. It was established for the first time that the alkoxy- and hydroxy-derivatives of polychlorobiphenyls obtained by chemical interaction with polyethylene glycols in the presence of alkali and with sodium methoxide contain a reduced amount of chlorine in the structure and are less thermostable compounds in comparison with the initial congeners of the Sovol technical mixture. It was found that heating the Sovol technical mixture leads to the evaporation of toxic polychlorobiphenyl congeners and the release into the atmosphere. During the thermal degradation of the obtained alkoxy- and hydroxy-derivatives of polychlorobiphenyls, there is no evaporation of PCBs congeners, and decomposition to the simplest environmentally acceptable volatile substances (CO 2 , H 2 O, HCl, etc.) is observed. Formation of polychlorinated dibenzodioxins and dibenzofurans is not detected. The proposed comprehensive two-stage approach to the destruction of technical mixtures of polychlorobiphenyls requires less energy and is characterized by a significant reduction in the emission of hazardous polychlorobiphenyls.