PhC-2022

Yu..Ya.. Gafner, D.A. Ryzhkova
Katanov Khakas State University

Abstract: The process of synthesis of CuAu nanoclusters from a high-temperature gas phase was simulated. The molecular dynamics method was employed, 1124 Cu and Au atoms were used as the initial configuration. The computer model of synthesis from the gas phase was based on an experimental setup located at the Budker Institute of Nuclear Physics SB RAS. On the basis of the data obtained, conclusions were made concerning the real chemical composition of clusters at the final stage of formation. It is shown that clusters larger than 400–500 atoms adhere to the given target ratio. The maximum deviations from the target ratio were recorded only for atomic vapor of stoichiometric composition. In other cases, with a reduction in the percentage of gold atoms in the initial pair, the deviations of clusters from the required composition decreased. It was determined that the reason for this was a different crystal structure of the nanoparticles obtained by modeling.
Keywords: nanotechnology, nanopowders, computer simulation, tight-binding potential, nanoparticles, copper, gold

E.S. Kartashynska
L.M. Litvinenko Institute of Physical Organic and Coal Chemistry

Abstract: The dependences of the molecular area (A_c) at the onset of the transition from the liquid-expanded to liquid-condensed (LE-LC) phase for 2D surfactant monolayer on the temperature and chain length are considered for seven surfactant classes at the air/water interface. A thermodynamic model of the amphiphilic monolayer behavior (taking into account the nonideality of mixing entropy) is used to evaluate A_c, as well as a quantum chemical approach that allows an assessment of the thermodynamic and structural parameters of surfactant associates. The calculated A_c values adequately reflect the experimental temperature dependence for the considered phase transition: the temperature increase leads to a decrease of the area per surfactant molecule with the fixed chain length and vice versa lengthening of the surfactant carbon chain at a fixed temperature results to the A_c value increase. The average values of the slope in the A_c = f(T) dependences for the regarded surfactant classes are in the range of 0,57-1,32 Ų/°C. The estimation of the (dA_c/dn)_T value shows that the best agreement of the calculated and available experimental data is achieved for saturated carboxylic acids and dialkyl-substituted melamine. The obtained results demonstrate applicability of the proposed approach for predictive purposes.
Keywords: 2D monolayer, clusterization Gibbs energy, unit cell, phase transition, thermodynamic model

A.Yu.. Kolosov, E.S. Mitinev, A.A. Taktarov, V.S. Myasnichenko, A.N. Bazulev, N.Yu.. Sdobnyakov
Tver State University

Abstract: The processes of melting and crystallization of bimetallic Pt- and Pd-based nanoparticles have been studied by the method of molecular dynamics. The possibility of obtaining stable nanoparticles containing 3000 and 4000 atoms in the temperature range from 500 K to 1600 K is established. The concept about the possibility of fixing the temperatures of starting and ending of the phase transition for melting and crystallization is confirmed which was put forward earlier for monometallic platinum and palladium nanoparticles. The analysis shows that during the cooling of Pd-Pt nanoparticles with an initially uniform distribution of components, formation of a mixed structure with a surface monolayer of Pd atoms is observed. The possibility of structural segregation in bimetallic Pd-Pt nanoparticles containing 3000 and 4000 atoms is shown. At the same time, these two sizes correspond to different scenarios. For bimetallic nanoparticles with 3000 atoms, local zones are mainly polyhedral, and for bimetallic nanoparticles containing 4000 atoms, formation of extended band structures is observed.
Keywords: molecular dynamics method, bimetallic nanoparticles, platinum, palladium, segregation, structural transformations, stability

P.V. Komarov^1,2, M.D. Malyshev^1,2
1 Tver State University
² A.N. Nesmeyanov Institute of Organoelement Compounds of Russian Academy of Sciences

Abstract: A self-healing epoxy material is considered, based on bisphenol A diglycidyl ether and atricarboxylic fatty acid hardener, belonging to a new class of polymers called vitrimers. The res toration of the integrity of such systems in the case of a damage occurs due to the exchange reaction of covalent bonds between the comonomers forming a polymer network. In our previous work, we have developed a model of this material based on the method of reactive dissipative particle dynamics. In this work, we apply our model to study the welding process of vitrimer samples cut into two parts. The control of the integrity of the structure of the systems was carried out using a topological analysis by calculating the distributions over the lengths of simple cycles and the density of the number of load-bearing circuits. It has been shown that the rate of restoration of the integrity of the systems is determined by the concentration of the catalyst and the degree of crosslinking of the polymer. The results obtained also indicate that in the case of a high degree of crosslinking of the polymer, as well as a low catalyst concentration, the structure of the system is highly inhomogeneous.
Keywords: vitrimers, network polymers, mesoscopic modeling, dissipative particle dynamics, bond exchange reaction

Yu..A. Kuznetsov, M.N. Lapushkin
Ioffe Institute

Abstract: The calculation of the density of states of various thicknesses of the 2D-layers of the intermetallic compound RbAu has been carried out. 2D-layers of intermetallic compound RbAu are simulated by supercells RbAu (111) 2×2×2. For a monolayer 2D-layer of an intermetallic compound RbAu the presence of a bandgap with a width of 2,70 eV has been established. An increase in the thickness of the 2D-layers of the intermetallic compound RbAu to three monolayers showed a decrease in the bandgap to 0,80 eV. A further increase in the thickness of the 2D-layers of the intermetallic compound RbAu leads to the disappearance of the band gap, which indicates a semiconductor-metal transition for the 2D-layer of the intermetallic compound RbAu with a thickness of four monolayers. The valence band of the 2D-layer of the intermetallic compound RbAu is formed mainly by Au 5d
electrons, with an insignificant contribution from Au 6s and Au 6p electrons. The conduction band of RbAu is formed mainly by Au 6p electrons with an insignificant contribution of electrons Rb 5s.
Keywords: electronic structure, ab initio calculation, intermetallic compounds, rubidium auride, 2D-layer

E.D. Kurbanova, V.A. Polukhin
Institute of Metallurgy of the Ural Branch of the Russian Academy of Science

Abstract: An analysis of synthesized unique two-dimensional 2D materials with nanolayer hexagonal and pentagonal structures (based on carbon, silicon, tin, binary compounds CN₂, BN₂, PdSe₂ and ternary compounds – BCN, CNP, PdSSe, Zn₂C₂P₂) was carried out. The synthesis of these materials was performed by the chemical vapor deposition or metal epitaxy on pre-prepared substrates. The strength and functional characteristics (electronic, optical) of the created models were also analyzed using the DFT theory in the form of triple monolayers with double-sided deposition of hydrogen on the surface of the p-Si₂C₄ monolayer: hydrogen/p-Si₂C₄/hydrogen. It was found that the p-Si₂C₄-4H layer with its two-sided hydrogen adsorption and good properties was the most dynamically stable. This article also presents relatively recently obtained hexa- and pentagonal two-dimensional materials not only for the elements C, Si, Ge, B, but also for Cu_1–xNi_x, Ti_1–xNi_x alloys and Bi_1–xSb_x, CN₂, BN₂, PdSe₂, etc. compounds. So, with the new unique materials created – the synthesis of superstrong, thermostable nanocomposites, superconducting layered composites (based on Bi, Hg and Sb), prospects are opening up for the development of nanoelectronics, spintronics, computer technology, as well as the creation of portable strain gauges, pressure sensors, gas sensors and dialysis catalysts for water dialysis with the release of hydrogen and oxygen.
Keywords: hexagonal and pentagonal structures of 2D materials, material modeling, mechanical properties, catalytic properties

R.M. Belyakova, E.D. Kurbanova, V.A. Polukhin
Institute of Metallurgy of the Ural Branch of the Russian Academy of Science

Abstract: The article presents both molecular dynamics calculations of binary Fe–Ni alloys and experimental studies of Ti and Co alloyed nanocrystalline alloys with a B2–Ti(Fe, Co) matrix structure as well as bcc-(Nb, Ti) and B2– eutectic phases Ti(Fe, Co). The structures of membrane alloys based on Fe–Ni (arrangement of atoms in coordination polyhedra and interatomic distances between atoms), as well as the kinetics of hydrogen – diffusion and permeability have been studied. It is shown that in the membranes of alloyed alloys with the substitution of Ni for cobalt Fe_35-XCo_XTi₃₅Nb₃₀, with an excess of Fe than for cobalt, mechanical brittleness is manifested in the B2–TiFe phase, and the plasticity of the B2 phase also decreases. At the same time, the resistance to an increase in hydrogen absorption is also weakened, up to mechanical destruction of membranes, so that in high-entropy alloys Fe_0,2Ni_0,2Cr_0,2Co_0,2Mn_0,2, Fe_0,2Co_0,2Cr_0,2 Ti_0,2Al_0,2 Fe and Co in equal parts. Other intermetallic alloys are also promising, having more complex compositions with high or moderate entropy, for example, Zr_0,2Ti_0,2Nb_0,2V_0,2Co_0,2 and Zr_0,2Ti_0,2Ta_0,2V_0,2Co_0,2, in addition to hydrogen evolution, also have storage properties. Within the framework of molecular dynamics, the effect of strain hardening of membrane HEA alloys is experimentally presented – the mechanism of synergy with multiple deformation. As a result of such hardening, a partial transformation of the austenitic phase into a
martensite phase occurs with the formation of twinning in their fcc/hcp grains and the formation of a two-phase matrix structure.
Keywords: nanocrystalline alloys, modeling, alloying, work hardening, matrix structure, eutectic phases, high-entropy alloys, austenite, martensite, membranes, hydrogen, hydrides

E.A. Bogdanova, V.M. Skachkov, K.V. Nefedova
Institute of Solid State Chemistry of the Ural Branch of RAS

Abstract: The article discusses the possibility of obtaining a hardened composite material with a porous structure based on nanostructured hydroxyapatite (HAP) synthesized by precipitation from a solution. The new material by the mechanochemical synthesis of HAP with reinforcing additives of titanium compounds was obtained. The synthesized samples are certified using some modern physico-chemical methods of analysis. The influence of the qualitative and quantitative composition of the composite on the sintering processes, porosity, strength characteristics, the degree of dispersion and morphology of the studied samples is shown. It has been experimentally established that a sample based on hydroxyapatite, reinforced with non-stoichiometric titanium dioxide of the composition Ca₁₀(PO₄)₆(OH)₂ – 15%TiO_x has the maximum strength characteristics and constant composition. The composite material, having a dense uniform structure with a high degree of crystallinity and a developed porosity, is a promising material for further research in order to introduce it into medical practice. A patent application has been filed on the developed composite material.
Keywords: hydroxyapatite, titanium oxide, titanium compounds, composite biomaterials, crystallinity, microhardness

A.N. Bolotov, O.O. Novikova, V.V. Meshkov
Tver State Technical University

Abstract: In the field of tribology, magnetic lubricating oils are promising, in which polymers are used to increase their colloidal stability, but their use is limited by the low magnetization of the colloid. It is possible to increase the magnetization of nanooils by synthesizing polymer shells directly on the surface of magnetic particles in the process of obtaining nanooils. The features of the technology for the synthesis of magnetic lubricating nanooils with polymeric solvation shells on particles, which protect them from coagulation, are described. Polymerization of hydroxy acid molecules proceeds by the mechanism of polycondensation on the solid surface of magnetite. The viscosity of the magnetic colloid increases due to the increase in the thickness of the solvate shell. Proceeding from this, a differential equation is proposed, which shows the dependence of the growth rate of the colloid viscosity on the rate of the polycondensation reaction. An experimental verification of the equation showed that it is fulfilled with an accuracy up to 8%. The resulting equation makes it possible to determine an important thermodynamic characteristic – the activation energy of the process of synthesis of polymer shells on the surface of dispersed particles. For calculations, it is necessary to
know the rate of change in the viscosity of a colloid with a dispersion medium without a monomer (hydroacid). Therefore, in the process of the polymer synthesis, samples of the intermediate magnetic colloid of a small volume are taken, which are used to determine the viscosity of the colloid and dispersion medium containing monomers. Then the viscosity of the colloid with a pure dispersion medium is found, which is necessary for calculating the activation energy of the polycondensation reaction. According to estimates, the error in determining the activation energy does not exceed 11%. In practice, using the values of the activation energy of polymerization, it is possible to carry out a purposeful choice of the optimal temperature-time regime for stabilizing the magnetic colloid in order to obtain a magnetic nanooil with the required viscosity and aggregative stability characteristics. Experimental studies were carried out on specially designed instruments for assessing the colloidal stability and dynamic viscosity of magnetic colloids.
Keywords: colloidal systems, magnetic lubricating nanooils, viscosity, colloidal stability, activation energy of polymerization

A.N. Bolotov, O.O. Novikova
Tver State Technical University

Abstract: The work is devoted to the study of processes occurring in the boundary lubricant layer, in which nanodisperse magnetic particles play a decisive or significant role. The friction between metal surfaces with lubricated oils of different concentrations of the magnetic nanodisperse phase was studied. The dispersion medium of magnetic oils consisted of liquids with various physico-chemical properties: dioctylsebacinate, triethanolamine, polyethylsiloxane. It has been shown that the wear intensity of surfaces with a hardness higher than that of nanoparticles monotonically increases with increasing the particle concentration, and wear is abrasive in nature. The wear rate of softer materials passes through a minimum at a particle concentration of about 2 vol.%. Magnetic separation of large agglomerates in oil allows for some time to reduce the abrasive wear until they are formed again under friction conditions. It was not possible to identify the regularities of the influence of nanodispersed particles on the friction force, it is probably insignificant. Several examples of the indirect effect of nanodispersed particles on the boundary friction are considered. In all the examples, the determining role plays huge area of the active surface of particles per unit volume of oil. For example, under conditions of friction, atomic hydrogen can be actively formed during the chemical interaction of fatty acids with the surface. Atomic hydrogen accumulates in the subsurface pores and is crystallized there. The increased pressure in the pores created by hydrogen molecules leads to an increase in wear by the peeling mechanism. The established regularities of the influence of nanodispersed particles on the rate of formation of the boundary lubricant layer and the corrosion wear of surfaces caused by surface-
active additives in magnetic oil are of scientific interest.
Keywords: nanodisperse particles, magnetic oil, grease, friction, wear