Numerical and analytical solutions of kinetic equations and the relevant equations for the moments of distribution of macroradicals and oligomers during radical chain polymerization are presented. It has been shown that the initial chain growth occurs in the ballistic mode involving first-generation primary radicals. The chain transfer in which a macroradical, reacting with a solvent, forms an oligomer and the primary radical of the next generation, causes a transition from the ballistic to the diffusion mode in which distributions of chains of different generations are mixed. Time-dependent distributions have been found for chain propagation and transfer rate constants independent of chain length.
The kinetic features of the oxidation–reduction processes of chromium ions during the treatment of potassium dichromate aqueous solutions with concentrations of 0.092–0.39 mmol/L in atmospheric-pressure dc discharge in oxygen at currents of 20–60 mA have been investigated. The solution served as the cathode of the discharge. It has been found that the discharge induces reversible Cr6+ ↔ Cr3+ redox reactions of chromium ions. The limiting degree of reduction of Cr6+ ions slightly depends on the discharge current and decreases with an increase in the initial concentration of the solution. The apparent rate constants of oxidation and reduction have been found, and the energy efficiency of the process has been evaluated. The obtained data are compared with previously obtained results for electric discharge in air and argon. It has been shown that the discharge in argon is the most effective for carrying out the reduction process.
The combination of dry distillation with irradiation with accelerated electrons can serve as a productive method for the conversion of waste plastics and their mixtures with cellulose wastes into liquid organic products. It was found that, on the combined distillation, plastics were mainly converted into soft wax and organic liquid. In turn, the lignocellulose fraction of mixed wastes was converted into furans (which can serve as raw materials for the subsequent synthesis of “green” plastics) and, in part, into phenolic inhibitors of reverse polymerization. The combined distillation is characterized by a lower yield of unsaturated and gaseous products, and it takes place at lower temperatures.
The effect of cucrbituril (CB7) on the redox reactions of thionine (ThH+) in the triplet state are considered in the absence and the presence of electron donor (FeSO4) and acceptor (p-nitroacetophenone). The formation of the 1 : 1 host–guest complex between thionine and CB7 increases the lifetime of the thionine triplet state. In the absence of exogenous electron donor and acceptor, the thionine triplet molecules in the host-guest complex enter into reactions of disproportionation and concentration quenching to give semioxidized and semireduced forms of thionine. The yield and lifetime of semioxidized and semireduced thionine forms exceed the yield and lifetime of these forms for free thionine. The complexation of thionine with CB7 decreases the efficiency of the thionine photoreduction and that of the reduction of the semioxidized form by the Fe2+ ions by factors of 5 and 2.5, respectively.
The dissipative processes of α-, β-, and μ-relaxation in irradiated acrylic latex polymers have been studied by means of dynamic mechanical relaxation spectroscopy. Radiation-induced changes in the temperature position of maxima and intensity of dissipative processes in the internal friction spectra of the polymers have been revealed. The manifestation of the effects depends on the rubber elasticity of the polymer and the presence of functional groups.
The process of hydrogen sulfide removal from methane with an admixture of C6–C8 n-alkanes in dielectric barrier discharge has been studied. It has been shown that the shortage of liquid hydrocarbon in the initial mixture results in the formation of high molecular polysulfide compounds, and an excess, in the formation of thiols and alkyl sulfides.
The influence of the conditions of mask-based photopolymerization of thick layers of a composition (with thickness h from 0.5 to 4.0 mm) based on dimethacrylate OCM-2 and o-quinone photoinitiator on the geometry of the resulting polymer sample has been studied. Upon photopolymerization of layers through a slit aperture of width l, the polymer formed has a cross section of trapezoid, the large base of which faces to the side of illumination. With increasing exposure, the difference in the sizes of the bases of the trapezoid decreases, which reduces roughness of an object composed of such layers. For stereolithographic synthesis of a 3D model from layers with h = 0.5 and 1.0 mm and roughness of 10 μm, the minimum slit width is achieved at l ≈ 2h.
The chain growth in radical chain polymerization is associated with the wave of transformation of primary radicals into macroradicals. The change in chain length n and molecular mass distribution R(t, n) with time t corresponds to the movement of a wave packet with velocity dn/dt and width ∆(n), both dependent on monomer concentration M(t). The formation of macroradicals in the absence of chain transfer when the rate constant of chain growth K(n) depends on n has been considered, and it has been shown that the packet is described by the Poisson distribution law with the event probability depending on K(n) and t. As K(n) decreases, R(t,n) narrows and its maximum shifts to the region of the minimum of K(n). Relations of K(n), M(t), and R(t, n) to dn/dt and ∆(n) have been found.
Using EPR spectroscopy, it has been established that monomers affect the decomposition rate of their polymerization initiators by forming complexes with them. Several structures of the complexes have been optimized, and their decomposition mechanisms, the activation energies of the chain initiation and propagation reactions, and the heat of polymerization have been determined by means of quantum chemistry methods. In the absence of radical inhibitors (evacuation), the polymerization proceeds with high efficiency (98%) at room temperature without stimulation of the system with external energy.
Polytetrafluoroethylene-based aerogel has been synthesized for the first time. Graphene oxide has been used as a binder. After reduction with hydrazine and annealing at 370°C, the aerogel surface has been found to become superhydrophobic (the contact angle of water is 162°). Superhydrophobic aerogel with a specific gravity of 30 mg/cm3 has been characterized by IR spectroscopy and X-ray photoelectron spectroscopy.
A CO oxidation catalyst that includes Pt clusters applied on nanosized TiN supports with a particle size of 18 and 36 nm has been synthesized. The catalyst has been studied using TEM, X-ray powder diffraction, and XPS methods. It has been found that platinum clusters formed on the support surface are covered with a mixture of platinum and platinum oxide. The coherent scattering range of the Pt cluster is close to 8 nm on a support with titanium nitride particles of 18 nm. The catalytic properties in the reaction of CO oxidation at 295 K and low CO concentrations (<100 mg/m3) have been examined. It has been found that when the platinum content in the catalyst is 9 to 15 wt %, the CO oxidation rate is 120 times higher than that on platinum black with a specific surface area of 30 m2/g. The catalysts are promising for use in catalytic systems for air purification.
Electrophysical parameters of atmospheric pressure discharge with an aqueous potassium permanganate solution as a cathode have been determined. The cathode potential drop, the electric field strength in the positive column of the discharge, and the current density depending on the solution concentration and the discharge current have been found, as well as the emission coefficient γ .
The effect of graphene doping with copper in a plasma jet reactor is studied. The effect is obtained during the synthesis of graphene in hydrocarbon-contating helium and nitrogen plasma jets generated by an electric arc plasma torch under reduced pressure. The graphene/copper nanocomposite synthesized has been studied by scanning electron microscopy, X-ray diffraction, and energy-dispersive X-ray microanalysis. It has been found that copper forms various bonds with carbon in graphene layers, which are due to interaction between the layers. It has been shown that the concentration of copper in the nanocomposite substantially depends on the composition of the plasma-forming gas and its flow rate.
A method for the synthesis of microdiamonds from graphite in an argon arc using germanium as a catalyst is presented. Simple microdiamonds and diamonds of complex configuration are obtained. It has been revealed that forms of synthesized nanomaterials are significantly affected by the buffer gas, the electrical and thermal parameters of the arc discharge, and the presence of germanium at the nucleation stage. Microdiamonds are formed within a few tens of seconds, which is much different from time required for their traditional production.
The photovoltaic composite formed by narrow-gap copolymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(bithiophene)] and methanofullerene [6,6]-phenyl-C-61-butyric acid methyl ester (PC61BM) has been studied in a wide energy range of generating photons, 1.32-3.14 eV at T = 77 K, by the light-induced electron paramagnetic resonance. It has been shown that some polarons are captured by spin traps formed in the copolymer matrix, and the concentration and depth of such traps are determined by the photon energy. The recombination kinetics of polarons and fullerene radical anions after turning off the light can be described in the framework of a second-order bimolecular process. The formation of spin traps in the copolymer matrix and the exchange interaction between different spin packets cause the extreme sensitivity of magnetic resonance and electronic parameters of charge carriers to the number and energy of generating photons.
The main operating modes of a radiofrequency induction plasma torch with a vortex stabilization of the atmospheric-pressure gas discharge at have been studied in an argon-hydrogen mixture in the range of Ar/H-2 = 12-4. The dependences of the electron temperature T-e and number density n(e) on the Ar/H-2 ratio have been experimentally studied. It has been found that the electron temperature and concentration in pure argon plasma are 0.88 eV and 7.6 x 10(14) cm(-3), respectively. When the Ar/H-2 ratio decreases, the electron temperature decreases to 0.42 eV, and the electron number density is 8 x 10(12) cm(-3). The calorimetric method used to estimate the gas temperature T-g, has given a value of 2500 K. The process of BCl3 reduction with hydrogen has been studied at the implemented operating modes of the induction plasma torch. The main products of the reduction of boron trichloride are a polycrystalline boron powder and dichloroborane. The morphology of boron and its phase composition and impurities have been studied. The average particle size of the boron powder is 200 nm.
When irradiation generates two radicals capable of initiating chain growth with different rate constants for chain transfer, two polymerization routes with different average chain length emerge. These pathways are not mixed in the initial part of the ballistic growth. Their mixing in chain transfer events is accompanied by transition from ballistic to diffusion growth. In the sol-gel transition region, the routes are spatially separated if the chain transfer depends on the rotational mobility of the reactants and decreases with increasing viscosity as the resulting oligomers accumulate. As an example, the polymerization of tetrafluoroethylene in solutions of silanes and oxysilanes is considered.
The kinetics of autoradiolytic degradation of the radiopharmaceutical drug 2[-[.sup.18]F]fluorodeoxyglucose [([.sup.18]F]FDG) in an air-saturated normal saline solution with initial activity concentrations of 1 and 2 GBq/mL has been studied. It has been established that the only radioactive product of radiation-induced transformations of [[.sup.18]F]FDG is [[.sup.18]F]fluoride, whose contribution in the total activity of the radiopharmaceutical increases with storage. It has been shown that an increase in the initial activity concentration of the radiopharmaceutical or a decrease in the concentration of ethanol in it leads to the enhancement of autoradiolytic degradation of [[.sup.18]F]FDG. However, an increase in the storage temperature of the solutions from 25 to 40[degrees]C does not affect the rate of radiation-induced dehalogenation of [[.sup.18]F]FDG.