Control of temperature field and residual stresses in growing basal-plane-faceted sapphire ribbons

The influence of different heat shielding constructions on the distribution of temperature and thermoelastic and residual stresses in growing basal-plane-faceted sapphire ribbons (Al₂O₃) is studied. It is shown that inclined shields decrease thermoelastic stresses owing to the redistribution of heat fluxes from a heater to a ribbon, which allows growing block-free basal-plane-faceted sapphire ribbons.     

Interaction of water-soluble polypyridylphenylene dendrimers with a polymethacrylate anion

Cationic water-soluble dendrimers have been prepared by the alkylation of pyridyl groups in polypyridylphenylene dendrimers of the first four generations, and their interaction with a polymethacrylate anion has been studied. The stability of polyelectrolyte complexes in aqueoussaline solutions has been studied by fluorimetric titration with the use of the pyrenyl-tagged polyanion, and it has been shown that the stability of these complexes significantly increases with the dendrimer generation number and the content of hydrophobic phenylene groups. Based on sedimentation analysis and turbidimetric titration, it is inferred that a significant part of charged groups of dendrimers are inaccessible to interaction with the polyanion and that water-soluble nonstoichiometric polyelectrolyte complexes develop in mixtures of higher generation dendrimers. Modeling results of this study may be useful for designing efficient cationic dendrimer carriers of genetic material and hydrophobic physiologically active compounds.     

On the thermodynamic theory of the strength of solids: 3. Thermodynamic linear tension of a crack in solid with dispersion forces

Th thermodynamic linear tension of rectilinear and curvilinear cracks in a solid with dispersion forces is calculated at the arbitrary value of the opening angle of a crack. The dependence of linear tension on the depth of the crack at depth and conformal mechanisms of its growth is analyzed. The effect of linear tension on the ultimate strength of a solid is evaluated and the known Griffith formula is generalized to the ultimate strength. It is shown that, in the case of rectilinear crack, the effect of linear tension on the ultimate strength is related to changes in linear tension during the growth of the crack, which is typical for a depth mechanism. For a curvilinear crack, this effect becomes twofold greater due to additional changes in the length of the frontal line of the crack in the course of its growth. The contribution of linear tension is negligible for macroscopic cracks, but can be equal to tens of percentage points for nanocracks demonstrating the beginning of the fracture of solids.     

New benzimidazole-2-yl-substituted polybenzimidazoles: Synthesis, properties, and hydrodynamic characteristics

The synthesis of novel benzimidazole-2-yl-substited polybenzimidazoles and initial compounds has been described. The polymers are studied by FTIR spectroscopy, TGA, and TMA. The hydrodynamic properties of macromolecules are investigated by translational diffusion and viscometry in 96% H₂SO₄; the molecular characteristics of the polymers are determined. Positive temperature dependences for intrinsic viscosities of the polymers are obtained. The polymers under study possess high hydrolytic stability with respect to sulfuric acid solutions up to 150°C and high thermal stability in the bulk. The TGA data correlate with the chemical structure of the polymers. The new polybenzimidazoles may be used as materials for the production of medium-temperature proton-conducting membranes.     

1,3,5‐Triphenyladamantane and 1,3,5,7‐tetraphenyladamantane

In 1,3,5‐triphenyladamantane, C₂₈H₂₈, (I), and 1,3,5,7‐tetraphenyladamantane, C₃₄H₃₂, (II), the molecules possess symmetries 3 and , and are situated across threefold and fourfold improper axes, respectively. The molecules aggregate by means of extensive C—H...π interactions. In (I), the pyramidal shape of the molecules dictates the formation of dimers through a `sixfold phenyl embrace' pattern. The dimers are linked to six close neighbors and constitute a primitive cubic net [H...π = 2.95 (2) and 3.02 (2) Å]. Compound (II) is isomorphous with tetraphenyl derivatives EPh₄ of group 14 (E = C–Pb) and ionic salts [EPh₄][BPh₄] (E = P, As and Sb). The multiple C—H...π interactions arrange the molecules into chains, with a concerted action of CH (phenyl) and CH₂ (adamantane) groups as donors [H...π = 3.15 (2) and 3.44 (2) Å, respectively]. The additional interactions with the methylene groups (four per molecule) are presumably important for explaining the high melting point and insolubility of (II) compared with the EPh₄ analogs.     

Asymmetric synthesis of phosphonotrifluoroalanine and its derivatives using N-tert-butanesulfinyl imine derived from fluoral

Addition of dialkyl phosphites to (S)-N-tert-butanesulfinyl imine derived from fluoral afforded, under mild conditions, the corresponding N-tert-butanesulfinyl α-aminophosphonates in moderate to high yields and diastereoselectivity. The major diastereomers of N-tert-butanesulfinyl α-aminophosphonates of (S_S,S) configuration were isolated, and after partial or complete deprotection, converted into enantiomerically pure phosphonotrifluoroalanine and its dialkyl esters.     

The development of the fundamental concepts of surface thermodynamics

Author’s results concerning the most fundamental problems of the thermodynamics of surface phenomena are reviewed. The generalized Laplace-Young-Kelvin equation, phase rules, and Gibbs adsorption equations are presented. Analogs of Konovalov’s laws are describes as applied to surface phenomena. The surface tension dualism, the Gibbs equation for adsorption on solid surfaces, and the phase equilibrium condition for a soluble nanoparticle are explained. The general mechanochemical approach, chemical affinity tensor, and the discovery of the mechanochemical dissolution effect are characterized. A novel approach to the monolayer state equation is formulated based on an excluded area. The problems of nucleation and the theory of surface separation are reperted.     

Structure and magnetic properties of the copper(II) complexes with diacyl hydrazides of salicylic acid

The structures and results of the static magnetic susceptibility investigation of the copper(II) binuclear complex with salicylic acid diacyl hydrazide (H₂L), [Cu₂(L)(Py)₄] (I), and the copper(II) trinuclear complex with diacyl dihydrazide of salicylic and glutaric acids (H₆L′), [Cu₃(L′)(Py)₄] · 2Py (II), are described. The exchange antiferromagnetic interactions between the paramagnetic centers with the exchange interaction parameter −2J = 119 cm⁻¹ for dimer I and 14 cm⁻¹ for trinuclear complex II are detected.     

Thermodynamic and Kinetic Foundations of the Micellization Theory: 4. Kinetics of Establishment of Equilibrium in a Micellar Solution

A system of the kinetic equations of the material balance for the concentrations of surfactant monomers and micelles in a micellar nonionic surfactant solution was formulated. The equilibrium state of a materially isolated micellar solution was analyzed. The system of the kinetic equations of the material balance of a micellar solution was solved. The total time of the establishment of equilibrium in a micellar solution was determined. It was shown that this time increases or (typically) decreases with an increase in micelle concentration, depending on the degree of micellization.     

Molecular and Crystal Structure of 5-Benzoyl-3-cyano-2-ethylthio-6-trifluoromethylpyridine

An X-ray diffraction structural analysis on 5-benzoyl-3-cyano-2-ethylthio-6-trifluoromethylpyridine was carried out to establish the regioselectivity of the reactions of ethoxymethylene derivatives of 1-aryl- and 1-hetaryl-3-trifluoromethyl-1,3-diketones with cyanothioacetamide and the alkylation pathway of the pyridinethiones obtained.