Vol 64, No 4 (2019)

The achievements in the study of the supramolecular structures arising in liquid crystals (LCs) under acoustic waves, which was started by the work of Professor А.P. Kapustin more than 50 years ago, are considered and generalized. The emphasis is on the problem of “threshold” destabilization of LC layer texture under mechanical deformations of different types generated by acoustic waves, which manifests itself in the formation of various supramolecular structures. Not only the factors determining the threshold characteristics of these structures for nematic and cholesteric LCs in a wide frequency range but also the dynamics of these structures above the threshold, as well as the specific features of their distortion under an acoustic binary effect are considered.

The triple-crystal high-resolution X-ray diffraction scheme has been experimentally and theoretically investigated using reciprocal space mapping. The procedure for calculating the spectral angular instrumental functions of diffractometer to take into account the influence of mirror, monochromator, analyzer, and slits on the intensity distribution near reciprocal lattice point is described. Good coincidence of calculated and experimental cross sections of reciprocal space maps (RSMs) is shown by an example of a perfect Si(110) single crystal.

An analysis of the diffraction patterns of powdered polytetrafluoroethylene (PTFE) γ-irradiated at room temperature in a nitrogen atmosphere to doses of 10–500 kGy with a fluence of 1.50 ± 0.3 Gy/s has shown that the diffraction peak 100 of the crystalline phase at 2θ ∼ 18° and the halo at 2θ = 10°–25° are most sensitive to ionizing radiation. It is found that the intensity, FWHM, and position of the maximum of reflection 100 change with an increase in the absorbed dose; this fact is indicative of the doublet nature of the peak profile. It is established that the doublet components differently response to ionizing radiation. The interplanar spacings, amplitude and sign of arising stress, and the degree of crystallinity (DOC) of polymer are calculated as functions of the irradiation dose. The radiation-induced change in the DOC of PTFE should be considered as a complex process, which includes radiative destruction and topochemical reactions of different types in crystals.

The results of investigation of the extended and broken symmetry substitution groups for elements of finite number sets are presented, with examples of the corresponding abstract structures, their computer visualization, and application in description of real structures. When studying the tables of binary transformations with broken symmetry in a computer experiment, transformation subsets (“evolutionary trees”) with convergent and divergent properties of structure oriented graph have been revealed.

A crystallographic analysis of SrAl₁₂O₁₉ (isostructural to BaFe₁₂O₁₉) and BaFe₁₈O₂₇ showed that the structures of both polytypes contain almost identical cationic and anionic (with participation of a large cation) sublattices, whose geometry is consistent with the high symmetry P6₃/mmc of these compounds. The presence of unified “skeletal” sublattices is considered to be the main condition for the formation of polytype structures.

Fracture regions in a nickel alloy have been investigated by electron microscopy. HfO₂ particles are mainly found in the fatigue crack zone. Their morphology and crystal structure are determined. The formation (with a relatively low concentration) of such particles and precipitates, containing Са, S, and other elements, is most likely related to the organic contamination of material.

It is shown that the Vlasov model for a solid describes the complexing processes when growing real crystals with allowance for the thermal growth conditions. It makes it possible (along with the classical theory of nucleation and growth of second-phase particles in solids) to calculate the defect crystal structure that was formed during the growth. It is established that the high-temperature impurity precipitation is directly related to the subsequent transformation of the defect structure when manufacturing of silicon devices. A qualitative model of the formation of electric centers is proposed, which directly relates their origin to the initial defect structure of silicon. It is shown that the concepts and principles of the Vlasov physics are absolutely applicable in solid-state physics.

A new modular eudialyte-group mineral—titanosilicate—from the Lovozero massif has been investigated using X-ray diffraction. The trigonal-cell parameters are found to be a = 14.069(4) Å, c = 60.63(1) Å, and V = 10393(1) ų; sp. gr. R\(\bar {3}\)m. The crystal structure is refined to final reliability factor R = 5.6% in the anisotropic approximation of atomic displacements using 1210F > 3σ(F). The idealized mineral formula (Z = 3) is Na₂₈Ca₁₂[Na_4.6][Mn_1.4]Ti₆[Si₅₂O₁₃₂(О,OH)₁₆](H₂O)_3.5Cl_1.5. The problems of the modular representatives of the group at the Zr–Ti isomorphism in the framework site and the Na–Mn isomorphism in the alluaivite module М2 sites are discussed.

[UO₂(suc)(C₂N₄H₄)₂] · 2H₂O (I) and [UO₂(Deaa)₄(H₂О)][(UO₂)₂(C₄H₄O₄)₃] · 2Deaa (II) crystals (suc^2– is succinate ion, C₂N₄H₄ is cyanoguanidine, and Deaa is N,N-diethylacetamide С₆Н₁₃NO) have been synthesized, and their IR spectroscopy and X-ray diffraction analysis have been performed. It is established that the I structure is formed by chains belonging to the crystallochemical group AQ⁰²M\(_{2}^{1}\) (A = UO\(_{2}^{{2 + }}\), Q⁰² = suc^2–, M¹ = C₂N₄H₄) of uranyl complexes. The II structure contains two types of complex groups: one-core cations [UO₂(Deaa)₄(H₂О)]²⁺ and layered anions [(UO₂)₂(suc)₃]^2–, with the corresponding crystallochemical formulas AM\(_{5}^{1}\) and A₂Q\(_{3}^{{02}}\) (A = UO\(_{2}^{{2 + }}\), M¹ = Deaa and Н₂О, Q⁰² = suc^2–). The nonvalent interactions in structure II and its carbamide-containing analog are analyzed by the method of molecular Voronoi–Dirichlet polyhedra.

DNA-Binding HU proteins are critical to the maintenance of the nucleoid structure and are promising pharmacological targets for the design of new antibiotics. The virtual screening for low-molecular-weight compounds capable of specifically interacting with the dimerization signals of two mycoplasma HU proteins was performed. The stability of target protein–ligand complexes was evaluated by molecular dynamics simulation. An analysis of the amino-acid environment of the ligands shows that inhibitors targeting the conserved amino-acid sequence, the so-called dimerization signal, which is involved in the formation of HU dimers and the maintenance of their stability and is located in an interdimer beta-sheet, have the second binding site in the alpha-helical domain. The binding determinants of inhibitors at the dimer interfaces of the proteins are identical and are independent of the amino-acid sequence. Consequently, HU proteins have two sites for the formation of the dimer interface, which should be taken into account in the design of inhibitors of dimerization.

Temperature dependences of internal friction Q^–1, obtained at different heating rates of a copolymer VDF/TrFE (75/25) sample, are studied in the temperature range of 290–420 K at a frequency f ≈ 16 Hz. It is shown that the maximum of Q^–1 observed in the vicinity of the ferroelectric phase transition (T_c = 393 K) is related to the motion of interphase boundaries and can be described within the low-frequency fluctuation mechanism of internal friction. The diffusion parameter σ of the ferroelectric phase transition is determined. The obtained σ value significantly exceeds the value that is due to possible microinhomogeneity of the chemical composition.

Temperature measurements (in the range of 375–830 K) of the ionic conductivity of terbium trifluoride single crystals (structure type β-YF₃) along three unit-cell crystallographic axes (a, b, and c) have been performed. It is found that TbF₃ crystals (orthorhombic system, sp. gr. Pnma) have a weak anisotropy of electrical conductivity: σ_||b/σ_||a = σ_||b/σ_||c ≈ 2. The conductivity along the b axis is σ_||b = 8 × 10^–6 S/cm at 500 K. The anisotropy of fluorine-ion conductivity in rare-earth fluorides with β-YF₃, LaF₃ (tysonite), and β-BaTm₂F₈ structures is discussed in the contest of the specific features of their atomic structure.

Shear surface acoustic waves, whose existence is due to the difference in the signs of piezoelectric modulus tensors of adjoining halves of crystal, are studied on flat interfaces of twinned hexagonal piezoelectric crystals of the \(\bar {6}\)m2 symmetry class. In this case, the inversion axis \(\bar {6}\) is perpendicular to the interface between the halves. It is shown that, at a weak piezoelectric effect, the characteristic penetration depth of these waves is inversely proportional to the square of component e₂₂₂ and may significantly exceed the length of the surface wave.

Orientation effects for crystalline nanoislands growing on dielectric surfaces are considered on the assumption of van der Waals interaction in the model of orientational phase transition with allowance for real crystallization conditions.

The spectral characteristics of a compound representing a new class of organic luminescent materials—dipyrrin oxophosphoryl complex (PODIPY)—in organic solvents and thin films have been investigated. The compound under study exhibits high-intensity fluorescence in solutions, which is preserved when passing to thin films obtained by layer-by-layer deposition onto a substrate using the Langmuir–Schaeffer technique. PODIPY is characterized by has bright solvatochromic fluorescence, which is related to the redistribution of the intensities of absorption and fluorescence bands and their shift. This effect originates from the specific solvation of PODIPY with partition of the oxygen atoms of oxophosphoryl group. A transition from solutions to films and an increase in the number of transfers lead to the fluorescence quenching without the formation of G aggregates in the film.

The structure of aqueous solutions of the Phospholipovit medicine, intended for transport of water-insoluble molecular drugs, has been investigated by small-angle neutron scattering. Phospholipovit can also be used alone, for example, in case of acute poisoning. When processing experimental data, neutron reflectometry was additionally applied to determine the scattering characteristics of maltose buffer solutions in which the medicine is stored. It is shown that Phospholipovit forms temperature-resistant (in the range of 20–37°C) vesicles of critically small size, with inner radius (~40 Å) comparable with lipid bilayer thickness (~31 Å), in these solutions. The sensitivity of vesicle parameters to an increase in the medicine concentration in solution (up to 25 wt %) and the character of vesicle interaction (indicating the presence of a significant charge on their outer surface) are determined.

Aqueous solutions of guanylurea hydrogen phosphite (GUHP) have been synthesized. The temperature dependence of equilibrium GUHP concentration in water was obtained. The change in the density of aqueous GUHP solutions with a change in their concentration was investigated. The influence of the solution pH on the GUHP solubility in water in the temperature range of +25–45°C was analyzed. The crystallization range of monoclinic GUHP crystals, belonging to the sp. gr. Cc, was determined. GUHP crystals were grown using different methods, based on cooling or maintaining a constant temperature, with mixing aqueous solutions or without mixing. The properties of the grown crystals in the optical and THz ranges were investigated.

New methods for growing LiIO₃ and Ba(NO₃)₂ crystals have been developed. Barium nitrate crystals up to 12 × 12 × 100 mm³ in size and lithium iodate crystals up to 120 × 120 × 200 mm³ in size of necessary optical quality are obtained. The influence of рН on the morphology of Ba(NO₃)₂ growth faces is investigated. The data on the morphology of the {111} and {\(\bar {1}\bar {1}\bar {1}\)} faces of crystals grown at different solution acidities are obtained by atomic force scanning microscopy. The possibility of fabricating optical elements from LiIO₃ crystals of ~100 × 100 × 100 mm³ in size is shown.

Self-consistent numerical model of laser cladding with coaxial powder injection has been developed. The model takes into account the heat transfer, hydrodynamics, solute transport, and phase transition kinetics. The additive process is numerically analyzed using the open-source computational fluid dynamics (CFD) package. The S-CLSVOF program is adapted for modeling heat and mass transfer and free boundary evolution of the melt pool. The phase transition is modeled using the Johnson–Mehl–Avrami–Kolmogorov equation with allowance for nonuniform temperature distribution on the melt pool surface. The clad-layer microstructure is investigated as a function of the process parameters. High scan rate is shown to result in a finer grain size of clad layer structure. The data obtained can be used for construct a cladding process map.