Vol 97, No 6 (2023)

A simple, highly accurate algebraic model is proposed for describing phase transitions on flat faces of square, hexagonal, and triangular structures. The model is derived using the cluster variational approach within the Ising model and expressed in an analytical form by choosing a basic closed-form cluster of the minimal size for each facet structure with nearest neighbors of z = 3 (triangular), 4 (square), and 6 (hexagonal). The new model provides three times more accurate equations for molecular distributions of particles in the Ising model than earlier analytical expressions. The model’s analytical equations allow direct calculations of molecular distributions. (Only iterative numerical means were used earlier to obtain results of the same accuracy.) The effect of refinements when considering correlation effects in the new model is compared to traditional mean-field and quasi-chemical (QCA) approximations when calculating isotherms and pair and cluster distribution functions. Analytical expressions are obtained for the critical temperature of a segregation-type phase transition.

Derivation and analysis of conditions of the thermodynamic stability for multicomponent reactive systems are proposed based on transformations and different representations of the stability matrix. Stability boundaries and spinodal conditions in systems with chemical interaction of compounds are discussed.

The behavior of L-lysine (Lys) in water and an aqueous buffer solution is studied by densimetry as the temperature varies from 288.15 to 313.15 K with an interval of 5 K. Based on the experimental density values of amino-acid solutions, the apparent molar volumes and partial molar volumes of Lys are determined at an infinite dilution in water and buffer solution at each temperature. The effects of temperature, medium, and amino-acid concentration on volumetric characteristics are revealed. The partial molar extensibility and their derivatives with respect to temperature, the values of which indicate the structurally destructive behavior of Lys in the studied solutions, are determined. It is found that the structurally destructive effects of Lys are enhanced in an aqueous buffer solution. It is shown that the partial molar volumes of amino-acid transfer from water to the buffer solution have positive values in the studied temperature range. The results obtained are discussed on the basis of various types of molecular interactions between a solute and a solvent using the Gurney model.

Special two-chamber setups are used to study the formation of xenon hydrates from a vapor–gas medium, depending on the volume of the chamber. The effect different parameters have on the growth of hydrates and the degree of saturation is studied. Hydrate growth conditions with saturation indices close to ideal are determined. Based on the experimental data, an estimate is made of the size of the crystalline hydrate nucleus (minimum size, 10–15 µm). It is established that for the emergence of such a nucleus from a vapor–gas medium, the required amount of steam at a temperature of 5°C is contained in a sphere 1 cm in diameter. Conditions are determined for the growth of a hydrate with saturation close to theoretical from a vapor–gas medium. It is shown that the rate of hydrate formation in a vapor–gas medium is several orders of magnitude higher than the one for liquid water. Raising the initial temperature of the vapor–gas medium increases both the rate of hydrate formation and the proportion of such hydrate.

The densities of binary and ternary mixtures of morpholine with dimethyl sulfoxide and N-methyl-2-pyrrolidone are experimentally studied at 293.15 K and atmospheric pressure, density deviations and excess molar volumes of mixtures are calculated from experimental data, concentration dependences for binary systems are described by the Redlich–Kister polynomial, and density isoline diagrams of the morpholine–dimethyl sulfoxide–N-methyl-2-pyrrolidone system are plotted.

Based on the example of solid-phase reactions of fullerenes with fluoride compounds of metals with a variable valence, the most important parameters of the kinetic model developed earlier by the author have been calculated. The model explains the selectivity of these reactions, which made it possible to obtain some C60 fullerene fluorine derivatives in an individual form, and opens ways to control them. For some of the reactions, a comparison was made with the data on the activation energy of elementary stages obtained earlier in the processing of mass spectral experiments. The estimates we made will contribute to the fine control of the conditions for a similar synthesis of other fullerene derivatives with small functional groups. They may also be useful in any long chain sequential reactions that produce broad gaseous or dissolved products.

Graphite intercalated compounds (GICs) with different stage numbers are prepared chemically from highly oriented pyrolytic graphite (HOPG), natural flaked graphite (FG) and nitric acid. Exfoliated graphite samples (EG-T) are synthesized from GICs via water treatment followed by thermal shock. The aim of this work is to investigate the dependence of the inner EG-T pore structure on the extent of oxidation and type of graphite by processing scanning electron microscopy (SEM) micrographs of EG-T cross sections. A procedure is developed on the basis of a deep convolutional neural network that speeds up image processing with no appreciable loss of accuracy. A strong correlation is found between EG-T pore structure parameters, the depth of oxidation, and the type of graphite.

A comparative assessment of the accuracy of determining the density and viscosity has been carried out for diisopropyl ether using the method of classical molecular dynamics using three potentials. The accuracy of determining the viscosity coefficients when using equilibrium and nonequilibrium calculation methods was also investigated.

The evolution of the electronic absorption spectra of substituted aluminum phthalocyanine incorporated into a nanoporous silicate gel matrix has been studied. The decomposition of the contour of the long-wavelength Q-absorption band of molecules into Voigt components reveals the dependence of the formation of various types of impurity sites in the matrix nanopores, which act as a solid-state nanoreactor, on the drying time of the matrix. Possible mechanisms of the effect of the internal structure of the synthesized silicate material during the transition from a sol state to a dried xerogel state on the spectral properties of phthalocyanine impurity molecules are discussed. Models of the interaction of the impurity molecules with the surface of the matrix nanopores during drying are considered; the features of the evolution of the resulting impurity sites are elucidated.

The reactions of neutral and anionic Au25(SCH3)12 clusters with one H2O2 molecule (mechanism I) and with its dimer (H2O2)2 (mechanism II) have been studied within the framework of the density functional theory (DFT). It has been established that all processes proceed with low activation barriers and a large gain in energy during the formation of products, and also that mechanisms I and II are interconnected. Based on the calculated data, the structure of gold clusters with the most probable active centers for further interaction with methane, which contain one or two O atoms, is proposed. In this case, clusters containing the O2 fragment can form not only in the reaction of the initial cluster Au25(SCH3)12 with hydrogen peroxide, but also with molecular oxygen, since the O2 adsorption energy is low and the process is close to equilibrium.

A current topical area of condensed matter physics is research in the field of structured materials that contain structures of micro- and nanoparticles. Electrospray is widely used to obtain micro- and nanoparticles. It is known to allow particles of different geometric shapes to be obtained. The authors propose an analytical procedure for obtaining a new class of nontrivial analytical solutions to the electrostatics problem of charge distribution over the surfaces of particles that can form while electrospraying. Complex nontrivial forms of this class of surfaces are considered. Exact analytical formulas are obtained for the charge distribution density over the surfaces of particles.

An experimental study is performed of the two-stage mechanochemical synthesis of niobium silicide. Theoretical estimates are made on the basis of the resulting macrokinetic model. The initial Nb + 2Si mixture is mechanically activated in the first stage, and the NbSi2 product is synthesized in the second. The effect the period of mechanical treatment has on the activated mixture’s morphology, temperature, and rate of burning is studied, along with the phase composition of the final reaction product. Kinetic constants are calculated that describe the dynamics of the two-stage mechanochemical synthesis of niobium silicide.

The results of studies of the polymorphism of the rodenticidal substance 2-[(4-chlorophenyl)phenylacetyl]-1H-indene-1,3(2H)-dione “chlorophacinone”, which has an anticoagulant mechanism of action, are presented. Methods for the synthesis of two new polymorphic forms (III and IV) have been established, for which data from physicochemical studies (IR, XRD) and information on the biological activity (toxicity) of polymorphs are given. Both forms crystallize in the monoclinic crystal system with space group P21/с and the following unit cell parameters: a = 16.698(1) Å, b = 5.632(1) Å, c = 20.253(2) Å, β = 109.65(1)° for III; and a = 9.853(1) Å, b = 9.041(1) Å, c = 20.474(1) Å, β = 97.322(3)° for IV. Polymorphic form IV with a toxicity parameter DL50 (gray rats) of 0.47 mg/kg has the highest biological activity versus 2.74 mg/kg for the less active form III. A method of identification of the most active form (IV) by IR spectroscopy was proposed.