Vol 53, No 2 (2019)

It has been established that radical polymerization of tetrafluoroethylene (TFE) in liquid alkoxysilanes (dimethyldimethoxy, trimethoxy, methyltrimethoxy, or tetramethoxysilane) yields fluorinated organosilicon oligomers with the general formula R(C₂F₄)_nH, where RH is an alkoxysilane molecule capable of further polycondensation. The composition of the terminal groups and the molecular-mass distribution of the oligomers have been determined from mass spectra, NMR spectra, and differential thermogravimetric curves. With increasing TFE concentration in solutions, the chain growth is accompanied by a transition from a homogeneous to a colloidal solution and then to a gel of oligomers. At maximum TFE concentrations, the chain length n in colloidal solutions reaches 10–12. The colloidal particles are composed of oligomers and solvent molecules, the number of which per one monomer unit is minimal in the gel to be 4–6. On the basis of the oligomers obtained, it is feasible to create coatings having both high hydrophobicity and strong bonding with the protected surface.

The mechanism of photochemical hydrogen atom transfer from an amine to a triplet nitro compound has been studied using monomethylamine and triplet nitromethane as an example. Two variants of the reaction have been considered: the transfer of hydrogen from the amino group and from the methyl group. The simulation has been carried out by quantum chemistry methods using the B2PLYP/cc-pVDZ functional. Complexation in pre- and postreaction complexes has been shown in terms of the theory of atoms in molecules. The profiles of potential energy surface of the reactions have been constructed. It has been concluded that the reaction of hydrogen transfer from the methyl group is energetically more favorable. It has been established that a strong hydrogen-bonded complex is formed during the reaction.

Sensitized phosphorescence of naphthalene-d₈ with a lifetime of 14.7 s at 22°C has been obtained in the supramolecular complex “naphthalene-d₈–β-cyclodextrin–cyclohexane–benzophenone” and attributed to T–T energy transfer upon excitation of benzophenone at 365 nm. The geometric structure of this complex, energies of singlet transitions, and oscillator strengths have been calculated by quantum-chemistry methods.

Large-scale computer simulation of the luminescence spectra of nanoclusters of CdSe colloidal quantum dots has been carried out, taking into account Förster resonance electronic excitation energy transfer between the nanoparticles. Quantitative dependences of the energy transfer efficiency on various parameters of the nanocluster have been obtained and analyzed in two model cases: a cluster of the nanoparticles with a specified size distribution and a cluster of a mixture of the monodisperse nanoparticles of two sizes. It has been shown that the dispersion of particle size distribution, the thickness of the protective ligand shell, and the fraction of nonluminescent particles in the cluster largely influence the energy transfer efficiency.

The radiation resistance of ceramic materials based on aluminum nitride have been studied. The irradiation has been performed at a temperature of 300 K using 40-keV C²⁺ ions with a fluence varied from 10¹⁴ to 10¹⁵ ion/cm². The dependences of crystallographic characteristics and strength properties on the ion fluence have been determined on the basis of X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray analysis data. It has been found that the irradiation results in the formation of an impurity phase Al₄C₃ in the surface layer, which leads to an increase in the lattice parameters. This finding indicates the implantation of C²⁺ ions and the formation of the interstitial phase in the structure.

A procedure for simulating gas-dynamic and thermal conditions during the conversion in a radiofrequency induction (RFI) plasma reactor has been developed. The model includes a turbulent flow of a mixture of ideal viscous compressible gases, taking into account inductive heating of the gas through heat conduction, convection, and radiation, considering the effect of the electromagnetic field force on the plasma motion. The formation of powder particles agrees with the results of thermodynamic calculations; the distribution of particles in the flow is described by the diffusion mechanism. The results of the simulation of the conversion of volatile boron chloride and boron fluoride in an RFI plasma torch with vortex-stabilized flow are presented.