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We study the aggregation of carbon allotrope nanofillers in the matrix of isotactic polypropylene with direct small-angle neutron scattering measurements. With the ATSAS software, we analyzed the d...

Appearance of the rheological explosion in PE pellets with different molecular weights is investigated. The duration of the first and second stages of the rheological explosion is almost independent of MW. The moment of irreversible destruction of the sample and the value of rheological explosion threshold linearly decrease with an increase in the length of the polymer chain. As a result of the explosion, the heat of melting of polymers with MW values equal to 3 × 105 and 1 × 106 decreases, while for PE with M = 3.5 × 104 the heat of melting remains almost unchanged. Electric current pulses are recorded. Their Fourier images are in the form of band spectra described by the Lorentz models for a damped harmonic oscillator and the Havriliak–Negami model for dielectric relaxation. Experimental data suggest that the rheological explosion is associated with the accumulation of elastic energy in the amorphous phase of PE and, during the rheological explosion, polymer chains are broken to generate radicals •RO2.

Low-temperature nitrogen adsorption, X-ray phase analysis (XRD), and electron microscopy are used to analyze the physicochemical properties (morphology, texture, phase composition, specific surface area, and porosity) of ASD-4 ultrafine powder and the products of the reaction between ASD-4 nanopowder and Mn, Fe, Co, and Ni formates. Results from studying the morphology and phase composition of oxidation products are presented, and the specific surfaces and porosities of the powders are calculated. Features of the adsorption isotherms of the studied samples after modifying them with formates are discussed in terms of their conformity to a specific type, according to the recommendations of the International Union of Pure and Applied Chemistry (IUPAC), and to certain types of porosity. The data show that the ASD-4 + 2% Mn and ASD-4 + 2% Ni samples are the ones with the highest adsorption activity. The specific surface area is 19.7907 m2/g for ASD-4 + 2% Mn and 10.1244 m2/g for ASD-4 + 2% Ni. The ASD-4 + 2% Mn and ASD‑4 + 2% Ni samples have more pores of mixed shape (slit-like and cylindrical) with widths of around 48.7234 and 44.2675 A, respectively. The pore volumes are 0.028250 and 0.012156 cm3/g for the ASD-4 + 2% Mn and ASD-4 + 2% Ni, respectively.

The possibility of determining the kinetic parameters of a reaction proceeding in a reactor with a fixed catalyst bed under critical conditions of ignition is demonstrated. The device of the measuring reactor and the consequences of ignition are described in detail. The proposed approach can be applied to corresponding variants of Fischer–Tropsch synthesis for hydrocarbons, along with other types of synthesis that employ fixed catalyst beds and high energies of activation. It is an easy way of determining the activity of catalysts.

The surface structure and volume of a 3D article produced by the method of selective laser melting from a powder of the D-16 alloy has been studied. Using the XPS method, it has been determined that there is an Al2O3 layer on its surface and a metal alloy Al–Cu with a copper content of ~5% under it, which coincides with the data of energy dispersive X-ray analysis conducted on the initial powder by the method of scanning electron microscopy. Local areas with an increased copper content (up to 13 at %) were revealed at the boundaries of the crystal grains. A high porosity of the obtained material has been established, which resulted from the specifics of crystallization of the Al–Cu system’s alloys related to the transfer of substance along the interfaces, as a consequence of the presence of concentration, temperature and, surface tension gradients along with nonoptimal 3D printing conditions.

The effect of induced mechanical activation of radio-frequency superradiance in a parametric mode under the action of an external rheological explosion at high pressure on a paramagnetic composite—a system of crossed spins based on binuclear complexes Co (QH)2–O–Co(QH)2 or Mn(QH)2–O–Mn(QH)2 (QH is a ligand based on 3,6-di-tert-butylpyrocatechol) in a polystyrene matrix—is found. Possible methods for processing data on the pulsed mechanical effect and a possible scheme of the initiation of the effect are proposed.

Based on the concept of collective vibrations of ions in the bulk of metal systems, the frequency of vibrations of an oxygen molecule on the aluminum–cerium alloy surface has been evaluated. Numerical estimation of the physical adsorption isobar has been carried out in accordance with the Henry law using these data and the heats of oxygen adsorption on the surface of this alloy in amorphous and polycrystalline states obtained on the basis of optical experiment data. It has been shown that changes in the alloy’s electronic structure upon splitting of the conduction band for the amorphous state has a significant effect on the qualitative characteristics of the adsorption process.

The effect of the modification of ASD-4 micron-sized aluminum powder by iron oxide on its oxidation in air was investigated. The metal particle surface was modified by coating with a gel based on Fe(OH)(HCOO)2 and ethylene glycol monomethyl ether, CH3OC2H4OH, with subsequent heat treatment in air. It was found that the presence of iron oxide generally had a positive effect on the oxidation dynamics of ASD-4 powder under heating in air. The oxidation rate of modified powders increases with increasing content of iron oxide in them. X-ray diffraction analysis using a synchrotron radiation source under heating to 1000°C showed the presence of only the basic phases of $$\gamma$$ -Al2O3and $$\alpha$$ -Al2O3, $$\gamma$$ -Fe2O3, and $$\alpha$$ -Fe2O3in the samples, and other iron oxides or intermetallic compounds were not detected. At a mass concentration of 10% Fe, an earlier appearance of the $$\alpha$$ -Al2O3phase was observed and the exothermic heat release peak was shifted to lower temperatures (893°C) compared to the unmodified ASD-4 powder (1045°C).

The frequency dependences of electrical conductivity with both real and imaginary components of a dielectric permittivity of polydimethylsiloxane oil suspensions filled by halloysite nanotubes having different amount of water are studied by dielectric spectroscopy. An analysis of frequency dependences of dielectric loss on temperature made it possible to assess the energy of activation of relaxation processes proceeded in suspensions. An effect of a low amount of water on the relaxation processes is considered.

The review examines the effect of radio-frequency superradiance during pulsed mechanochemical activation of polymer composites under high pressure. Mechanochemical activation is implemented in three modes: (a) rheological explosion of polymer composite under rapid uniaxial compression, when an elastic wave pulse occurs in a polymer composite sample and implements the physico-chemical transformations leading to the occurrence of a superradiance pulse; (b) parametric mode, when an elastic wave pulse is introduced from the outside through a waveguide into a composite sample; (c) the mode of rapid pressure release, which also leads to the occurrence of a superradiance pulse. Paramagnetic polymer composites—namely polystyrene–binuclear clusters Co(QH)2–O–Co(QH)2 or Mn(QH)2–O–Mn(QH)2, where QH is a ligand based on QH2–3,6-di-tert-butylpyrocatechin)—are considered as objects implementing such processes. These binuclear clusters exhibit the Dzyaloshinskii–Moriya effect, and polymer composites based on them exhibit multiferroic properties. A composite of a molecular magnet in polystyrene matrix (Eu(III)(SQ)3·bipy complex with four unpaired electrons on Eu(III) and on SQ ligands; SQ is 3,6-di-tert-butylquinolate paramagnetic ligand) is also considered. The binuclear clusters and europium complexes form 2D nano-objects in the polymer matrix with a diameter of 50–100 nm and a thickness of ~ 1–2 nm. The review considers the formalisms of Dicke, Lorentz, Landau–Lifshitz–Blombergen and Havriliak–Negami equations, which make it possible to conduct a time–frequency analysis of these processes, to obtain data on the relaxation processes of spin and charge density in objects responsible for the process of radio-frequency superradiation. It is also shown that the analysis of electron spin resonance data allows us to provide a probable quantum chemical scheme for the implementation of the radio-frequency superradiance process. The phenomenon of superradiation has a great deal of potential in such areas as energy-saving technologies, wireless power transmission and storage devices. The technique of studying fast mechanochemical processes considered in the review allows us to investigate the mechanisms of interaction of magnetic and electrical subsystems in multiferroics and molecular magnets, which expands the scientific base for the creation of new functional materials and enables the solving of related problems of condensed matter physics.

In this review, we summarize recent developments in the field of the mechanochemistry of polymers. The aim of the review is to consider the consequences of mechanical forces and actions on polymers and polymer synthesis. First, we review classical works on chemical reactions and polymerization processes under strong shear deformations. Then, we analyze two emerging directions of research in mechanochemistry—the role of mechanophores and, for the first time, new physical phenomena, accompanying external impulse mechanical actions on polymers. Mechanophores have been recently proposed as sensors of fatigue and cracks in polymers and composites. The effects of the high-pressure pulsed loading of polymers and composites include the Dzyaloshinskii–Moriya effect, emission of superradiation and the formation of metal nanoparticles. These effects provide deeper insight into the mechanism of chemical reactions under shear deformations and pave the way for further research in the interests of modern technologies.

This paper presents carbon nanotubes-containing polymer composites with layered gradient structure having electromagnetic interference (EMI) shielding properties. Polymer composite films we...

X-ray diffraction with the help of synchrotron radiation is used to analyze a sequence of phase formation in the oxidation of original and modified Al powders in the case of heating in oxidizing gaseous media with rates of 10 and 100 K/min. It is established that an increase in the heating rate of the modified ASD-4 powder leads to an active growth of metastable phase (θ- and δ′-Al2O3) of aluminum oxide except for the γ-Al2O3 phase. Assumptions about the forms of existence of vanadium in the interaction products are given. It is shown that diffusion limitations in the core—shell system (Al-Al2O3) can be removed under the action of an oxidizing aluminum particle on physicochemical processes at interphase boundaries.

The electron structures of pure and oxidized aluminum surfaces at ambient temperature have been studied while analyzing the results of a simulation of optical conductance on the basis of optical experiments. It is established that oxidation of an aluminum surface in the solid state leads to splitting of the conduction band when it contains forbidden state regions. The heat of oxygen adsorption on aluminum stated has been determined on the basis of properties of surface states.

The effect of small additives of manganese, iron, cobalt, and nickel oxides on the oxidation of aluminum powder of ASD-4 grade while heating in air is studied. Composites of Al/MOx were prepared by impregnating the metal powder with saturated solutions of M(HCOO)2 ⋅ 2H2O (M = Mn, Fe, Co, and Ni) formates and thermal treatment of the mixtures in air with a maximum annealing temperature of 375°C. It has been established that the effect of modifiers on the intensity of oxidation depends on the nature of the interfacial interaction on the surface of particles. The formation of a liquid phase in the interaction of aluminum oxides and iron leads to the loss of the protective properties by the barrier layer of oxidation products and acceleration of the process.

Dielectric properties of two series of magnetoactive elastomers (MAEs) based on a soft silicone matrix containing 35 vol% of magnetic particles were studied experimentally in a wide temperature range. In the first series, a hybrid filler representing a mixture of magnetically hard NdFeB particles of irregular shape and an average size of 50 μm and magnetically soft carbonyl iron (CI) of 4.5 μm in diameter was used for MAE fabrication. MAEs of the second series contained only NdFeB particles. The presence of magnetically hard NdFeB filler made it possible to passively control MAE dielectric response by magnetizing the samples. It was shown that although the hopping mechanism of MAEs conductivity did not change upon magnetization, a significant component of DC conductivity appeared in the magnetized MAEs presumably due to denser clustering of interacting particles resulting in decreasing interparticle distances. The transition from a non-conducting to a conducting state was more pronounced for hybrid MAEs containing both NdFeB and Fe particles with a tenfold size mismatch. Hybrid MAEs also demonstrated a considerable increase in the real part of the complex relative permittivity upon magnetization and its asymmetric behavior in external magnetic fields of various directions. The effects of magnetic filler composition and magnetization field on the dielectric properties of MAEs are important for practical applications of MAEs as elements with a tunable dielectric response.

The adsorption properties of an unmodified ASD-4 aluminum powder and the powder modified with a V2O5 hydrogel are studied via low-temperature nitrogen adsorption. Special purity grade nitrogen is used as the adsorbate. Adsorption isotherms are measured, the specific surface area and porosity of the powders are calculated, and the results from morphological studies are described. The dependence of the structural and adsorption properties of the nanopowders on their composition is shown. Due to the island structure of the xerogel, the specific surface area of the modified aluminum powder is greater than that of the unmodified material by several tens of times. The specific surface areas of the ASD-4 and ASD-4–1% V samples are 0.6511 and 16.8752 m2/g, respectively. It is found that the layered structure of the deposited xerogel ensures the formation of mesopores with a size of 45 A in the modified sample.

Data on the effect of electromagnetic fields on polymerization processes are analyzed and integrated. The results of investigation of the response of polymeric systems including polymerization mixtures, polymer solutions, melts and gels to external electromagnetic fields are discussed. Mechanisms of changes in the kinetic parameters of cationic polymerization of certain monomers are considered. They are based on ideas of spatial redistribution of growing macroions and counterions depending on the degree of dissociation of the active sites, which can lead to an increase in the polymerization rate, stabilize it or slow down the process. It is shown that these mechanisms are universal for other ionic systems. Almost all types of polymerization processes are discussed to reveal potential fields of their application in additive manufacturing technologies. High demand for further studies of the effect of electromagnetic fields on polymeric objects is pointed out in connection with the need to solve problems in the design of novel materials and functional structures. The bibliography includes 214 references.

The sequence of phase formation in the oxidation of ASD-4 aluminum powder modified by vanadium pentoxide during heating in air in the temperature range 873–1073 K has been studied by synchrotron radiation x-ray diffraction. It has been shown that the sharp acceleration of the oxidation of the modified powder is related to the loss of the protective properties of the oxide shell on the particle surface due to the polyvalence of vanadium, which provides structural and phase changes on the surface and in the depth of the oxidized metal.

A magnetoelectric effect was discovered in polystyrene/organoelemental binuclear cobalt complexes with ligands of spatially hindered phenols at room temperature. The Dzyaloshinskii–Moriya interaction (dipole–dipole and anisotropic exchange interaction of unpaired electrons on cobalt ions at 77 K and room temperature) is fulfilled in such complexes. A novel class of high-temperature multiferroics—polymer composites—can be produced on the basis of such molecular structures.

A novel nanocluster (organosilicon dendrimer - copper dimer) G1–8S-Dec•2CuCl2 was synthesized by a mechanochemical method. Optical and IR spectroscopy, NMR and ESR methods confirm that mechanochemical action on the mixture (dendrimer G1–8S-Dec + anhydrous copper (II) chloride) leads to the formation of a structure in which two copper atoms are linked by exchange interaction and are stabilized in the form of a dimer by sulfur atoms in the structure of the dendrimer G1–8S-Dec. A quantum mechanical calculation was carried out using the density differential method (DFT), which proved the possibility of the existence of two tetrahedral complexes SCuCl3 connected by a common face of chlorine atoms and having sulfur atoms at the vertices located in the branches of the dendrimer. The structure of the Cu2Cl4Si5C116H244S8 nanocluster is calculated by complete geometry optimization. It was found that the synthesized cluster implements the Dzyaloshinsky - Moriya interaction and exhibits multiferroic properties.

The results of a reactivity study of aluminum powders modified with surfactants of different natures allowing one to decrease the protective properties of an oxide film on a particle surface during heating in the oxidizing medium are given. Ca, Ba, and V2O5 used as modifiers were shown to allow considerably increasing the completeness and rate of oxidation of ASD-4-type aluminum powders used as fuels in composite propellant compositions. The mechanism of action of modifiers on the oxidation and combustion of disperse aluminum was established.

A new class of high-temperature multiferroics has been created. They are polymer composites based on a polystyrene matrix and nucleus–shell nanoparticles, where the nucleus consists of silica nanoparticles and the shell consists of Fe(III) spin-variable ions.

Two catalytic systems, metallocene-based and Ti-based were used to synthesize by in situ polymerization the composites of polypropylene and few-layer graphene nanoparticles, prepared by chemical or thermal reduction of graphite oxide. The effect of metallocene and titanium catalytic systems on the properties of nanocomposites and distribution of nanoparticles in polymer matrix is investigated in detail. The data on electrical and thermal properties of nanocomposites are presented. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers

We present the results of dielectric measurements for toluene solutions of cooper (II) carboxylates (valerate, isovalerate, undecylate, myristate, stearate, benegate). We have measured for the first time the electric capacity Cp at various concentrations of these carboxylates in toluene in the solution temperature range.

The synthesis, structure, and electrophysical properties of a polymer-inorganic biocompatible composite based on unsaturated chitosan ether, namely, allyl chitosan, and vinyltriethoxysilane are studied. During composite synthesis, allyl chitosan forms an individual nanophase with vinyltriethoxysilane and its condensation products in the polymer matrix of allyl chitosan. The size of nanoparticles embedded in a polymer matrix increases from 50 to 1000 nm as the fraction of the added vinyltriethoxysilane grows. Under exposure to UV radiation, both homopolycondensation and heteropolycondensation occur in the composite films via crosslinking according to the radical mechanism and the composite becomes insoluble in water. It has been shown that the resulting composites feature ionic conductivity under application of both direct current and high-frequency electric fields to the sample. Conductivity is provided by a proton–electron ensemble that concentrates at the nanoparticle/polymer matrix interface.

A magnetoelectric effect has been found at room temperature in a polymer composite—polystyrene–metal–organic manganese dimers with ligands of spatially hindered phenol. It is shown that these metal-organic manganese dimers implement the Dzyaloshinskii–Moriya interaction and are weakly ferromagnetic. It is suggested that a new class of high-temperature multiferroics can be created on the basis of such molecular structures.

The adsorption and structural features of Al–5% Pb alloy powder before and after reacting with water are analyzed. Results from studying the morphology and phase composition of the oxidation products are presented, and the specific surface area and porosity of the powders are calculated. It is shown experimentally that water treatment of Al–5% Pb alloy powder even at room temperature leads to the formation of new phases and affects the powder’s morphology. It is established that a major role in the properties of the watertreated powders is played by nanopores that form between crystallites on a particle’s surface during waterinduced oxidation and subsequent thermal dehydration.

Poly(p-xylylene) – titanium thin film nanocomposites were synthesized by vacuum deposition polymerization and proposed to serve as a gas sensor. They can reversibly and selectively detect several parts per thousand water, ethanol and even n-propyl benzene vapors with short response time. The presence of polar molecules affects conductance and capacitance, while nonpolar vapors such as benzene and toluene have no effect on electrical properties. Polarization and depolarization currents were recorded and it was found that composition of gaseous medium affected the parameters of dielectric response function. The frequency dependences of complex capacitance were fit by the Debye equations; correlations of the fit parameters and titanium concentration, as well as dipole moment of analyte molecules in atmosphere were found. The model was proposed, that explains dielectric behavior of nanocomposites and assumes the existence of several dielectric relaxation processes with different characteristic times: orientation of physically adsorbed polar molecules, charge exchange of surface states, generated by chemisorbed molecules at the interface nanoparticle/polymer matrix and Maxwell-Wagner interfacial polarization phenomena.

The self-organization of detonation nanodiamond particles in dielectric liquid polydimethylsiloxane has been studied by broadband dielectric spectroscopy. Frequency dependences of the conductivity and the complex modulus of dielectric permittivity were measured. The structure of nanodiamond suspensions has been studied by small-angle X-ray scattering as well. Electrophysical properties of detonation nanodiamond suspensions, namely conductivity and permittivity, strongly depend on the particle surface chemistry. The temperature dependences show the activation nature of polarization processes. The model explaining observed effects has been proposed.

In view of the great practical utility of aluminum–rare earth metal (REM) powders as adsorbents and catalyst supports, the dispersion composition and morphology of Al–3%Y alloy powder particles obtained by various methods (gas plasma recondensation, nitrogen sputtering) were studied by low-temperature nitrogen adsorption, scanning electron microscopy, XRD, etc. The phase composition of the powders was determined, and the amount of active aluminum was calculated. The nitrogen adsorption on the powder surface was studied experimentally at–196°С at relative pressures of Р/Рs = 10–3–0.999. The specific surface areas of the powders were determined.

This research investigates polystyrene mixtures with nanosized surface-modified particles, i.e., molecular silicasol, silsesquioxane, and first-generation carbosilane dendrimer. Three types of similarly sized particles with the same type of surface layer possess different chemical structures and rigidities of the cores. The latter is defined not by the numerical value of the elastic modulus but is based on the concept of molecular mobility of the chemical bonds that form the core. The phase and rheological behaviour as well as the relaxation and dielectric properties of the systems were investigated. The viscosity and the glass transition temperature of the systems decrease with increasing filler content but do not depend on the core rigidity of the particles. However, the molecular structure of the core of a hybrid nanoparticle defines both its own elastic modulus and the elastic modulus of the whole composite as well as affects the rate and activation energy of the segmental motion in the polymer. The characteristics of the composite depend on the core rigidity of the nanoparticles if the correlation radius of the physical characteristic is comparable to or less than the nanoparticle radius. The organic surface layer of nanoparticles serves both as a compatibilizer of the polymer-nanoparticle system and as a peculiar type of a “solvent” in the polymer matrix.

Composite materials of polypropylene, graphene nanoplatelets (GNP) or fullerene C60 were synthesized by in situ polymerization. GNP particles consist of 3–5 graphene layers and have aspect ratio 40. In composites with pristine GNP particles their aspect ratio is 110, whereas ultrasonic processing reduces it to 40–50. This change of aspect ratio of filler particles and their aggregates results in different properties of composites with pristine and sonicated GNP. Percolation threshold for composites with pristine GNP is 0.25% vol. In composites with sonicated GNP it is 2–3% vol. This is due to reduction in the size of filler particles aggregates and more uniform distribution of particles in polymer matrix after ultrasonic treatment. The presence of nanocarbon filler (GNP or fullerene) makes α-transition, associated with the glass transition of the amorphous phase of polypropylene, clearly resolved. Its intensity increases with the concentration of nanofiller, which acts as a dielectric probe. POLYM. COMPOS., 36:1006–1011, 2015. © 2015 Society of Plastics Engineers

Reaction mixtures in which polymerization processes proceed are investigated both in an electric field and under classical conditions. The observed kinetic effects are explained using a model concept of the primary contribution to the revealed field effects from the dissociation of ion pairs due to the spatial redistribution of ions. This model may be applied to both cationic and anionic polymerization processes.

The effect of the phase composition of an aluminum-based alloy powder containing 1.3% barium and the products of its interaction with air on the kinetics and mechanism of oxidation was first studied by x-ray diffraction using synchrotron radiation. It is found that the high surface and reactivity of barium lead to the activation of aluminum oxidation due to the heterogeneity of the phase composition of the barrier layer of the reaction products on the particle surface.

The effect of the phase composition of an aluminum-based alloy powder containing 1.3% calcium and the products of its interaction with air on the kinetics and mechanism of oxidation was first shown by x-ray diffraction using synchrotron radiation. It was found that the high surface and chemical activity of calcium led to an increase of more than a factor of two in the completeness of the process in the temperature range of 1300–1550 K upon heating at 10 K/min.

Adsorption of nitrogen on Al-3% La, Al-1.5% Sc, and Al-3% Ce powders before and after processing with water in the relative pressure range p/ps = 10∼3 to 0.999 is experimentally studied at a temperature of 78 K. It is shown that the interaction between ultradispersed powder and water depends on the properties of the original powder, including the original content and composition of the oxide-hydroxide phases in the surface layers of metal particles, and the length and conditions of storage. Results confirming that processing powders containing rare-earth metals with water at room temperature leads to the formation of new phases and affects their morphology are presented. It is shown that the nanopores formed between crystallites on the surface of the particles during oxidation with water and subsequent thermal dehydration play an important role in the properties of powders processed with water. The specific surface and the porosity of powders are calculated.

Dielectric characteristics of polytetrafluoroethylene (PTFE) films modified by direct current discharge at the anode and cathode have been studied as a function of frequency and temperature. It has been found that the dielectric constant increases slightly as a result of plasma treatment and weakly depends on temperature. It has been shown that the frequency dependences of conductivity at 20°C differ somewhat for the original and treated films, but the closer resemble one another at 80°C, with the difference in the critical conductivity indices becoming more significant.

In this work the possibility of forming nanocomposite materials based on polyethylene oxide and hybrid organo-inorganic “core-shell” systems known as molecular silicasols with a modified external layer is studied. The chemical structure of a particle shell similar to the polymer matrix monomeric unit allows one to decrease the surface tension on the disperse phase-disperse medium interface. The level of compatibility of the components and its influence on the molecular weight of the polymer matrix was estimated based on interferometry and viscometry data, as well as an analysis of the concentration dependence of MFI, dielectric, and mechanical properties of the composites.

Polystyrene-based composites containing hybrid molecular silica sol nanoparticles with a core-shell structure are studied during fast compression. Polystyrene and the related composites are found to fail instantaneously at a certain critical pressure, which is accompanied by the emission of electromagnetic and acoustic waves. The composite composition changes the critical pressure during explosion and the frequency characteristics of the generated electromagnetic and acoustic waves. The charge density transfer mechanism in a composite with a filler concentration higher than 10 wt % is shown to differ from that in composites with a lower filler content.

Composite materials of isotactic polypropylene and graphene nanoplatelets were synthesized by in situ polymerization in liquid propylene with the use of metallocene catalyst system. Graphene nanoplatelets were prepared by chemical oxidation of graphite and subsequent reduction. Preliminary ultrasonic treatment of GNP suspensions in toluene results in better dispersion of particles, both in liquid polymerization medium and in polymer matrix. GNP particles consist of 3–5 graphene layers and have aspect ratio 40. In composites with pristine GNP particles their aspect ratio is 110, whereas ultrasonic processing reduces aspect ratio to 40–50. Ultrasonic processing provides, apparently, a more uniform distribution of GNP particles, which in nanocomposite are largely individualized. This change of aspect ratio of filler particles and their aggregates results in different properties of composites with pristine and sonicated GNP. Percolation threshold for composites with pristine GNP is 0.25 vol.%. In composites with sonicated GNP percolation threshold is 2–3 vol.%. This is due to reduction in the size of filler particles aggregates and much more uniform distribution of particles in polymer matrix after ultrasonic treatment.

The effect of a constant magnetic field up to 6000 Oe on transient current after application of a pulsed voltage of U = 5 V with a duration of 100 μs is studied for composites based on polyaniline, manganese acetylacetonate, barium oxide hexahydrate, gadolinium chloride, and elemental sulfur. Initial powders are mixed in a ball mill. The giant magnetoresistance with a magnitude of 40–60% is discovered. It manifests itself as a difference in transient-current curves in the absence of the magnetic field and in its presence. This effect is explained by spin-dependent transport, in which at least two charge assemblies are involved: namely, electron assemblies and proton assemblies.

Nanocomposites of polypropylene and graphene nanoplatelets were synthesized by in situ polymerization in liquid monomer in the presence of highly effective isospecific homogeneous metallocene catalyst. Microstructure, mechanical, dielectric, and thermal properties of composites are presented. X-ray phase analysis data indicate that graphene nanoplatelets are present in composites as thin flaky particles aggregates, with aspect ratio affected by sonication of reaction mixture. Crystallization tempera- ture of polypropylene increases in composites. Nanocomposites are characterized by high rigidity, thermal stability, and crystalliza- tion temperature, low conductivity, and high dielectric losses in the microwave range. V C 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 127: 904-911, 2013

Composites based on polystyrene (PS) and core-shell hybrid nanoparticles of molecular silica sol are studied during fast compression. At a certain critical pressure, PS and the related composites are found to fail instantaneously. This process is accompanied by the emission of electromagnetic and acoustic waves. The sample composition and the filler particle size change both the critical pressure during explosion and the frequency characteristics of the appearing electromagnetic and acoustic waves. The fracture of PS and the related composites is accompanied by the formation of a fibrillar structure.

The oxidation features of powdered metals associated with the presence of a barrier layer of reaction products on the particle surface is considered. It is shown that phase formation processes, the stresses resulting from an increase in film thickness during heating, and the thermal stresses on the oxide-metal interface lead to fracture of the protective layer, which affects the oxidation kinetics. A mechanism for the interaction of aluminum alloys with rare earth metals and Ca and Ba with air under programmed heating and the processes determining the reaction kinetics is proposed based on an analysis of their previously investigated physicochemical properties and experimental data on the oxidation of powders of these systems of various dispersity. The effect of particle size and alloying on the nature of the processes is studied.

New composite materials containing polyaniline, sulfur, manganese acetylacetonate, lanthanum chloride, and praseodymium chloride are obtained. The components are blended and subjected to mechanochemical treatment in a ball mill; then, the composites are molded into thin films. Application of an external magnetic field with a strength of 6000 Oe leads to an increase in the conductivity of the films by more than 3000% to reach the properties of materials possessing giant magnetoresistance. An analysis of the time dependences of transient current under application of direct voltage to the samples indicates the presence of charge carriers of three types: presumably, e−, H+, and Cl−. A possible mechanism for the development of the giant magnetoresistance effect in the obtained composites is discussed.