Polyimides (PIs) are materials that are resistant to high temperatures and crucial for the manufacturing of films, fibers, coatings, and 3D-printed items. PIs are widely used as electrically insulating materials in electronics and electrical engineering. This study investigated how the chemical structure (i.e., choice of initial monomers), the synthesis conditions of the prepolymer (i.e., choice of amide solvent), and the conditions for forming polyimide films (i.e., final curing temperature) affect the thermophysical properties and short-term electrical strength of obtained polyimide films of different chemical structures. In this work, we varied the compositions of the dianhydrides used for synthesizing polyamic acids—pyromellitic acid (PMDA), tetracarboxylic acid diphenyl oxide (ODPA) and 1,3-bis(3′,4-dicarboxyphenoxy)benzene acid (R)—with a constant diamine: 4,4′-oxydianiline (ODA). Additionally, we varied the amide solvents employed: N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP). This study represents the first investigation into how the choice of solvent in the synthesis of thermoplastic polyimide prepolymers affects their short-term electrical strength. The molecular weights of the polyamic acids were determined using gel permeation chromatography (GPC). The deformation and strength characteristics of the investigated films were also assessed. The thermophysical properties of the polyimides were evaluated via dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). X-ray diffraction analysis and infrared spectroscopy (IR) were conducted on the examined film samples. The short-term electrical strength was also evaluated.

Composite films were synthesized by radical copolymerization of styrene with methacrylate groups on the surface of modified single-walled carbon nanotubes. Mechanical grinding and reforming of films on the electrode led to a decrease in the electrical resistance values by two magnitude orders. This effect was observed when measuring the current-voltage characteristics in both sandwich and planar structures. This decrease in the electrical resistance of the composite films is likely due to the disintegration and reorientation of carbon nanotubes, as well as the creation of mechanical stresses in them as a result of covalent bonding to the polymer matrix, which could affect the electronic structure of carbon inclusions.

Zr1-xYxO2-0.5x nanoparticles were introduced into the sulfonic acid form of the Nafion-type perfluorinated copolymer prior to membrane formation to improve its water retention, thermal stability, and proton conductivity. Since the conditions under which nanoparticles are formed can significantly influence their size, phase composition, morphology, and surface chemistry, various approaches to filler synthesis were considered in this study. It was found that among the wet-chemical methods used to produce zirconia-based nanoparticles, solvothermal synthesis offers the most promise in terms of increasing the surface proton conductivity of composite membranes. This method ensures small size, large specific surface area, and high hydrophilicity of the nanoparticles. Consequently, their incorporation into a Nafion-type perfluorinated copolymer increases the membrane's moisture retention and improves to its proton-conducting properties. In the case of Zr1-xYxO2-0.5x nanoparticles formed under solution combustion conditions, their more hydrophobic surface did not contribute to an increase in the moisture content of the perfluorinated copolymer, but did allow its maximum operating temperature to be increased by 20 C-degrees.

Ferromanganese formations are widespread in the Earth’s aquatic environment. Of all the mechanisms of their formation, the biogenic one is the most debatable. Here, we studied the Fe-Mn crusts of hydrothermal fields near the underwater volcano Puy de Folles (rift valley of the Mid-Atlantic Ridge). The chemical and mineralogical composition (optical and electron microscopy with EDX, X-ray powder diffraction, X-ray fluorescence analysis, Raman and FTIR spectroscopy, gas chromatography—mass spectrometry (GC-MS)) and the magnetic properties (static and resonance methods, including at cryogenic temperatures) of the samples of Fe-Mn crusts were investigated. In the IR absorption spectra, based on hydrogen bond stretching vibrations, it was concluded that there were compounds with aliphatic (alkane) groups as well as compounds with double bonds (possibly with a benzene ring). The GC-MS analysis showed the presence of alkanes, alkenes, hopanes, and steranes. Magnetically, the material is highly coercive; the blocking temperatures are 3 and 13 K. The main carriers of magnetism are ultrafine particles and X-ray amorphous matter. The analysis of experimental data allows us to conclude that the studied ferromanganese crusts, namely in their ferruginous phase, were formed as a result of induced biomineralization with the participation of iron-oxidizing and iron-reducing bacteria.

The present paper is devoted to the investigation of the formation process and growth of Gd2Ti2O7 nanocrystals with a pyrochlore structure doped with Sm3+ and Nd3+ ions. During the Gd2Ti2O7:Sm3+/Nd3+ nanoparticles synthesis, aqueous solutions of gadolinium, samarium and neodymium nitrates were added to a mixture of titanium isopropoxide, and polyethylene glycol was diluted with isopropyl alcohol, after which the resulting substance was evaporated to a gel state and heat-treated according to a two-stage scheme. As a result of the study, it has been shown that the forming material had a trabecular structure with a developed network of macro- and micropores. The use of a two-stage heat treatment promotes uniform distribution of different nature atoms in resulting samples. In addition it has been concluded that gadolinium titanate crystalls with a pyrochlore structure is formed by an aggregation mechanism at 700 °C from an X-ray amorphous precursor. From the point of view of obtaining a single-phase material, a possibility of varying nanocrystals dimensions and the pyrochlore structure defectiveness, annealing of the precursor in the temperature range of 750–900 °C is most promising. In this case, the most significant percentage of Sm3+ and Nd3+ ions, which change their localization with increasing synthesis temperature, are incorporated into the crystal structure of Gd2Ti2O7. Doping of Gd2Ti2O7 nanocrystals not only leads to appearance of expected photoluminescence, but also contributes to manifestation of extraordinary effects in dielectric characteristics of such a material.

In this paper, we report on novel polyimide (PI) nanocomposites filled with binary mixtures of metal oxide (either TiO2 or ZrO2) nanoparticles and nanocarbon (either carbon nanofibers (CNFs) or functionalized carbon nanotubes (CNT(f)s)). The structure and morphology of the materials obtained were comprehensively studied. An exhaustive investigation of their thermal and mechanical properties was performed. We revealed a synergistic effect of the nanoconstituents with regard to a number of functional characteristics of the PIs compared with single-filler nanocomposites, including thermal stability, stiffness (below and above glass transition temperature), yield point, and temperature of flowing. Moreover, the possibility of manipulating the properties of the materials by choosing a proper combination of the nanofillers was demonstrated. The results obtained can become a platform in the design of PI-based engineering materials with tailored characteristics capable of operating in extreme conditions.

The transition from 'the initial graphite material, consisting of multilayer graphene of macroscopic size, to its oxidized form occurring as films, followed by their thermal reduction in an atmosphere of hydrogen, allows for obtaining submicron galleries of reduced graphene oxide with oxygen-containing groups on the surface. Such hydroxyl and carboxyl groups were used to functionalize the surface of graphene nanosheets with methacrylate groups to twist graphene layers relative to each other during in-situ copolymerization with styrene. In such a composite, mechanical stresses and defects are potential in the graphene nanosheets, which may be the reason for local superconductivity at room temperature. A similar effect was also recorded for photoreduced graphene oxide with a perforated surface as a component of a pol-ystyrene-based composite.

The surface morphology, structural organization, and transport properties of composite membranes based on Russian Nafion-type perfluorinated copolymers filled with zirconium dioxide nanoparticles are studied using atomic force and scanning electron microscopy, X-ray structural analysis, and thermal analysis. A relationship between the morphology of the free surface and the “substrate” surface of Nafion-LSC-1 proton-conductive film membranes and the concentration of zirconium-dioxide nanoparticles (ZrO 2 ) is found. Atomic force and scanning electron microscopy reveals a gradient in the concentration of zirconium-dioxide nanoparticles, with the highest concentration on the substrate side of the membrane. The free surface is characterized by the presence of two phases alternating over the surface area of the membrane, which may be due to the presence of hydrophilic and hydrophobic regions. Zirconium nanoparticles form associates with sizes up to 300 nm. Wide-angle X-ray diffraction data suggest that Nafion-LSC-1 composite membranes have a mesomorphic structure when the concentration of zirconium-dioxide nanoparticles is 1.6 wt %, while the precursors of these membranes are characterized by a crystalline structure. The samples of Nafion-LSC-1 and composite membranes filled with 0.53, 1.12, and 1.61 wt % of nanoparticles are characterized by moisture content, proton conductivity, and heat resistance.

Cobalt ferrite nanoparticles were synthesized both in hydro and in solvothermal conditions from Co and Fe salts of different chemical nature (nitrates and chlorides) taken in a 1:2 cation ratio. Varying the chemical prehistory, synthesis temperature, isothermal holding time, and the reaction medium composition made it possible to obtain a set of Co x Fe 3 − x O 4 nanoparticles of different average diameters and isomorphic substitution degree x . The resulting nanoparticles’ elemental composition, crystal structure, sizes, and magnetic properties were determined using EDX analysis, X-ray diffraction, transmission electron microscopy, and SQUID magnetometry. The temperature dependences of the coercivity, remanent magnetization, squareness on both the average diameter and the stoichiometry of nanoparticles are considered. Co x Fe 3 − x O 4 nanocrystals ranged from 11 to 29 nm were single magnetic domains and showed ferrimagnetic behavior at room temperature. The hardest magnetic nanoparticles with maximum squareness values in the high-temperature region were formed with x = 0 . 79 using solvothermal treatment of cobalt and iron nitrates at 250 ◦ C, 7 MPa for 10 hours.

This article is devoted to the study of the processes of formation and growth of nanocrystals with the pyrochlore structure in the TiO2-Gd2O3 system. A mixture of an aqueous solution of gadolinium nitrate and a solution of titanium isopropoxide with polyethylene glycol in isopropyl alcohol was evaporated to a gel state, and then it was heat-treated using a one- or two-stage scheme. The study showed that the material being formed has a trabecular structure with a developed system of macropores. The use of the two-stage roasting method allows a uniform distribution of titanium and gadolinium atoms in the sample. Gadolinium titanate with a pyrochlore structure, which is formed using an aggregation mechanism at a temperature T = 700 degrees C from an X-ray amorphous precursor, is a variable composition compound. It has been shown that in terms of obtaining a monophasic product, the possibility of varying the size of nanocrystals, and defects in the pyrochlore structure, the most promising heat treatment mode is synthesis in the temperature range of 750-900 degrees C. In this case, the possibility of controlling the above characteristics of Gd2Ti2O7 nanoparticles can be implemented by varying the ratio of titanium- and gadolinium-containing precursors in the initial mixture, the duration of the isothermal exposure process.

This paper is a corrigendum related to the article Vasil'ev B.V., Smyslov R.Yu., Kirilenko D.A., Bugrov A.N. Synthesis and magnetic properties of cobalt ferrite nanoparticles formed under hydro and solvothermal condition. Nanosystems: Phys. Chem. Math., 2021, 12 (4), P. 492-504, http://nanojournal.ifmo.ru/en/articles-2/volume12/12-4/chemistry/paper11/

Inks for 3D printing were prepared by dispersing bacterial cellulose nanofibers (CNF) functionalized with methacrylate groups in a polymerizable deep eutectic solvent (DES) based on choline chloride and acrylic acid with water as a cosolvent. After 3D printing and UV-curing, the double-network composite gel consisting of chemically and physically crosslinked structures composed from sub-networks of modified CNF and polymerized DES, respectively, was formed. The rheological properties of inks, as well as mechanical and shape memory properties of the 3D-printed gels, were investigated in dynamic and static modes. It was shown that the optimal amount of water allows improvement of the mechanical properties of the composite gel due to the formation of closer contacts between the modified CNF. The addition of 12 wt% water results in an increase in strength and ultimate elongation to 11.9 MPa and 300%, respectively, in comparison with 5.5 MPa and 100% for an anhydrous system. At the same time, the best shape memory properties were found for an anhydrous system: shape fixation and recovery coefficients were 80.0 and 95.8%, respectively.

A series of multiblock polyurethane-ureas (PUU) based on polycaprolactone diol (PCL) with a molecular mass of 530 or 2000 g/mol, as well as hard segments of different lengths and structures, were synthesized by the step-growth polymerization method. The chemical structure of the synthesized multiblock copolymers was confirmed by IR- and NMR-spectroscopy. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) were used to determine the relaxation and phase transition temperatures for the entire series of the obtained PUU. The X-ray diffraction (XRD) method made it possible to identify PUU compositions in which the crystallizability of soft segments (SS) is manifested due to their sufficient length for self-organization and structuring. Visualization of the crystal structure and disordering of the stacking of SS with an increase in their molecular mobility during heating are shown using optical microscopy. The change in the size of the hard phase domains and the value of the interdomain distance depending on the PCL molecular mass, as well as the length and structure of the hard block in the synthesized PUU, were analyzed using small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS). The evolution of the domain structure upon passing through the melting and crystallization temperatures of PUU soft blocks was studied using SANS. The studies carried out made it possible to reveal the main correlations between the chemical structure of the synthesized PUU and their supramolecular organization as well as thermal and mechanical properties.

Cellulose nanofibers (CNF) produced by bacterial were functionalized along the surface with 3-(trimethoxysilyl)propyl methacrylate (TMSPM). The chemical and crystalline structure of the material was confirmed with NMR, FTIR, EDX and XRD methods. Modified CNF were used as a crosslinker and reinforcer for polymerizable deep eutectic solvent (DES) based on acrylic acid and choline chloride. Dispersions of modified nanofibers in DES were applied as UV-curable ink for 3D printing. It was shown that shielding of -OH groups of the cellulose surface with TMSPM increased the quality of 3D printed filaments due to reduced CNF agglomeration. At the same time, surface methacrylic groups copolymerize with acrylic acid forming crosslinked ion gel. Elastic moduli of the prepared ion gels were identical to those of gels based on unmodified CNF and crosslinked with N,N'-methylenebisacrylamide. However, strength and the ultimate elongation of the material prepared in this work were 1.05 ± 0.08 MPa at 2700% that is significantly higher than those of the material prepared with unmodified CNF.

A series of polyimide/metal oxide (either ZrO2 or TiO2) nanocomposite films were fabricated based on two polymer matrices. The prepared films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray diffraction analysis (XRD), and their thermal and mechanical properties were investigated with the use of thermogravimetric (TGA), differential thermal analysis (DTA), and thermomechanical analysis (TMA). We have found out that functional properties of the obtained materials are determined by a number of factors, not only the type, size, surface functionality, and concentration of the nanofiller, but also the chemical structure of the matrix polyimide. We have demonstrated some trends in the thermal and mechanical behavior of the materials depending on these features. The data could be of great interest in the areas where new materials with improved functional characteristics are needed.

The use of reduced graphene oxide (r-GO) is a promising way of fabricating organic–inorganic composites with unique electrical and magnetic properties. In our work, polystyrene/r-GO composites were synthesized, in which both the components are linked together by covalent bonds. The r-GO used differs from the graphene obtained from graphite through mechanical exfoliation using the ‘scotch tape’ by presenting many structural defects. Binding in the composite structure between the components was confirmed by infrared spectroscopy. Elemental analysis was carried out by energy dispersive X-ray spectroscopy. Scanning electron microscopy, X-ray diffraction, and Raman spectroscopy were used to monitor the 2D-order in exfoliated r-GO galleries. Using a vibrating-sample magnetometer, we have shown that the composite magnetization loops demonstrate type-II superconductivity up to room temperature due to r-GO flakes. We believe that a strain field in the r-GO flakes covalently binding to a polymeric matrix is responsible for the superconductivity phenomena.

The scale of magnetic correlations in materials based on reduced graphene oxide (RGO) has been estimated for the first time using the method of small-angle scattering of polarized neutrons. This information cannot be obtained by other methods. Experiments have demonstrated the presence of small-angle magnetic-nuclear interference scattering for both original RGO and an RGO-based composite in magnetized fields H about 1 T, which unequivocally indicates the presence of magnetized areas on the scale of 1000 Å in the studied materials.

This study investigates the thermal and structural properties of multilayer composites based on chitosan (CS) and polyanions with different functionalities, including sodium sulfoethyl cellulose (SEC), sodium alginate (ALG), and sodium hyaluronate (HA). Unlike polyelectrolyte complexes (PECs) obtained by polymer mixing, the formation of a PEC layer by a process of layer-by-layer deposition of oppositely charged polymers is accompanied by the transformation of the CS polymorphic state, and this affects the relaxation and thermal properties of the resulting multilayer composite. X-ray diffraction analysis showed that the formation of the PEC layer in the CS/SEC multilayer film is accompanied by crystallization of the CS chains and the formation of a predominantly anhydrous CS modification. Thermogravimetric analysis of the CS/SEC film registers a high-temperature peak associated with the thermal decomposition of crystalline CS in the PEC composition. According to the dynamic mechanical analysis, the CS/SEC composite was characterized by a single glass transition temperature, indicating a strong interaction between the layers when using SEC (a strong acid salt) as the counterion to CS. For multilayer composites with weak polyacid salts (ALG and HA), the crystallization of CS in the PEC layer is weaker, as reflected in the thermal degradation of these films. A high-temperature peak is recorded in the thermal decomposition of CS/HA and is absent in the case of CS/ALG. Dynamic mechanical analysis of the CS/ALG composite showed two glass transition temperatures close to those of the original polymers, indicating weak PEC formation. The CS/HA composite showed an intermediate response. Thus, the effect of the PEC layer on the properties of the poly-layer composites decreases in the order CS/SEC > CS/HA > CS/ALG.