Сверхизлучение и синтез наночастиц металла в полистирольном композите с многоспиновыми комплексами Eu при быстром одноосном сдавливании

Composites of heterospin molecular magnet [EuIII(SQ)3bipy] in a polystyrene (PS) matrix have been synthesized. This complex [EuIII(SQ)3bipy] contains four paramagnetic centers - the Eu3+ ion and three SQ ligands (SQ—3,6-di-tert-butyl benzoquinone radical anion); bipy (bipyridyl) is diamagnetic. It has been established that intensive mechanical activation of [EuIII(SQ)3bipy]/PS samples leads to an reological explosion, as a result of which radio frequency superradiance, the appearance of free electrons and the formation of Eu metal nanoparticles are observed. The duration of this process is 10 ns.

Electron paramagnetic resonance in organic binder aging in dispersely reinforced substructures

Purpose: To study the intensity of binder aging in organo-mineral mixtures using electron paramagnetic resonance. The aging intensity of the organic binder is provided by its concentration in paramagnetic centers, since asphaltenes are almost one hundred percent of paramagnet concentration and indicate to the aging intensity of the petroleum dispersion system.Approach: Dispersed reinforcement of substructures with chemical fibers made of spent sorbents containing a controlled amount of absorbed oil products allows to partially solve the problem of crack formation and fracture of road pavements designed in accordance with the regulatory documents.Research implications: The service life of substructure made of dispersely reinforced organo-mineral mixtures reduces owing to organic binder aging, which begins at the stage of preparation of organo-mineral mixtures and continues during the substructure operation. Organic binder ageing results in the formation of solvation layers on the surface of mineral materials that become more viscous and brittle.Findings: The substructure dispersed reinforcement with chemical fibers made of spent sorbents containing a controlled amount of absorbed oil products decreases the concentration of paramagnetic centers. This indicates to a decrease in the asphaltene concentration, thereby reducing the aging intensity of the oil dispersion system.

Effect of Diamond Polishing and Thermal Treatment on Carbon Paramagnetic Centers’ Nature and Structure

Diamonds contain carbon paramagnetic centers (stable carbon radicals) in small concentrations (at the level of ~1 × 1012 spins/mg) that can help in elucidating the structure of the nitrogen atoms’ contaminants in the diamond crystal. All diamonds that undergo polishing are exposed to high temperatures, owing to the friction force during the polishing process, which may affect the carbon-centered radicals’ concentration and structure. The temperature is increased appreciably; consequently, the black body radiation in the visible range turns orange. During polishing, diamonds emit an orange light (at a wavelength of about 600 nm) that is typical of a black body temperature of 900 °C or higher. Other processes in which color-enhanced diamonds are exposed to high temperatures are thermal treatments or the high-pressure, high-temperature (HPHT) process in which the brown color (resulting from plastic deformation) is bleached. The aim of the study was to examine how thermal treatment and polishing influence the paramagnetic centers in the diamond. For this purpose, four rough diamonds were studied: two underwent a polishing process, and the other two were thermally treated at 650 °C and 1000 °C. The diamonds were analyzed pre- and post-treatment by EPR (Electron Paramagnetic resonance), FTIR (Fourier transform infrared, fluorescence, and their visual appearance. The results indicate that the polishing process results in much more than just thermal heating the paramagnetic centers.

EPR study of paramagnetic centers in SiO2:C: Zn nanocomposites obtained by infiltration of fumed silica with luminescent Zn(acac)2 solution

Silica-carbon with zinc (SiO2:C:Zn) nanocomposites obtained via infiltration with aged luminescent zinc acetylacetonate (Zn(acac)2) ethanol solution of two concentrations (1 or 4%) into the fumed silica (SiO2) matrix have been studied using EPR within the temperature range 6…296 K before and after thermal annealing. The EPR spectrum of SiO2:C:Zn nanocomposites consists of three signals with the Lorentzian lineshape corresponding to paramagnetic centers with S = 1/2, which are related to carbon dangling bonds (CDB) (g = 2.0029(3)), silicon dangling bonds (g = 2.0062(3)) and oxygen-centered carbon-related radicals (CRR) (g = 2.0042(3)). A small EPR linewidth (<1 mT) observed for CDB and oxygen-centered CRR allows us to conclude that they are in the sp3-hybridized state. It was found that the temperature dependence of the EPR signal integrated intensity of the CDB and oxygen-centered CRR follows the Curie–Weiss law with a small positive value of the Curie–Weiss constant, which indicates that the weak ferromagnetic exchange interaction takes place in the spin system of CDB and oxygen-centered CRR. It was supposed that the carbon-related centers are clustered in SiO2:C:Zn nanocomposites. We assume that the oxygen-centered CRR in the sp3-hybridized state are associated with luminescent centers in previously reported aged Zn(acac)2/C2H5OH solution.

Jellyfish-like few-layer graphene nanoflakes: high paramagnetic response alongside increased interlayer interaction

Jellyfish-like graphene nanoflakes (GNF), prepared by hydrocarbon pyrolysis, are studied with electron paramagnetic resonance (EPR) method. The results are supported by X-ray photoelectron spectroscopy (XPS) data. Oxidized (GNFox) and N-doped oxidized (N-GNFox) flakes exhibit an extremely high EPR response associated with a large interlayer interaction which is caused by the structure of nanoflakes and layer edges reached by oxygen. The GNFox and N-GNFox provide the localized and mobile paramagnetic centers which are silent in the pristine (GNF p ) and N-doped (N-GNF) samples. The change in the relative intensity of the line corresponding to delocalized electrons is parallel with the number of radicals in the quaternary N-group. The environment of localized and mobile electrons is different. The results can be important in GNF synthesis and for explanation of their features in applications, especially, in devices with high sensitivity to weak electromagnetic field.

Direct observation of hyperpolarization breaking through the spin diffusion barrier

Dynamic nuclear polarization (DNP) is a widely used tool for overcoming the low intrinsic sensitivity of nuclear magnetic resonance spectroscopy and imaging. Its practical applicability is typically bounded, however, by the so-called “spin diffusion barrier,” which relates to the poor efficiency of polarization transfer from highly polarized nuclei close to paramagnetic centers to bulk nuclei. A quantitative assessment of this barrier has been hindered so far by the lack of general methods for studying nuclear polarization flow in the vicinity of paramagnetic centers. Here, we fill this gap and introduce a general set of experiments based on microwave gating that are readily implemented. We demonstrate the versatility of our approach in experiments conducted between 1.2 and 4.2 K in static mode and at 100 K under magic angle spinning (MAS)—conditions typical for dissolution DNP and MAS-DNP—and directly observe the marked dependence of polarization flow on temperature.