Photoalignment dynamics of azo dyes series with different coordination metals

There are many photoaligned azo dyes that can be used for orientation of liquid crystals in various display devices. However, the structure of these compounds needs to be optimized to increase the rate of the process of molecule photoalignment, as well as to spread the application of these compounds. The main coordination metal that presents in the molecules of azo dyes is sodium derivatives. The use of other alkali metals remains an open question. We used quantum‐chemical computation methods and reversible intermolecular bonding model to determine the effect of metal coordination on the velocity of photoalignment. The theoretical predictions were experimentally verified using sodium, potassium, lithium, and cesium salts of the model azo dye synthesized by us. We conclude that potassium azo derivatives are the fastest, ceteris paribus.     

New Refractories Developed by the Ukrainian Research Institute of Refractories Named after A.S. Berezhnoy

The article gives an introduction to the Ukrainian Research Institute of Refractories and especially its R D and refractory products for the industries of iron and steel,nonferrous,glass and chemistry etc.     

DYNAMIC TENSIONS IN FINITE OIL DROPLETS

In reacting systems, dynamic interfacial tension (IFT) values above 10-20 mN/m are often encountered. For such high tension values, infinitely long oil droplets will not be realised in spinning drop tensiometry. Hence, Vonnegut's solution will not be strictly valid. The experimentalist is then compelled to use one of the several alternative solution schemes proposed in the literature. We have obtained dynamic IFT data for 0.3125 mM oleic acid in hexadecane contacted with various NaOH solutions by the use of a novel experimental scheme called photo-micropendography. These tension values were then compared with spinning drop tensiometer data calculated by using three alternative solution schemes, namely, Vonnegut's method, the formula of Slattery and Chen and the analysis of Princen el al. The comparison showed that when the droplet's length/width ratio was below 2.5, Vonnegut's formula was severely in error. The solution scheme proposed by Slattery and Chen gave tension values close to those found by photo-micropendography over the entire range of IFT values exhibited by the oleic acid/caustic systems. However, the most consistent and reasonably accurate tension values resulted from the use of Table I in the paper by Princen, Zia and Mason. A simplified computer algorithm has been proposed for calculating dynamic interfacial tensions using the formulas and tables proposed by the latter authors. However, at length/width ratios above 2.5, the agreement between interfacial tensions determined by micropendography and spinning drop data calculated by the use of Vonnegut's solution was quite good.     

An NMR‐MOUSE® for Analysis of Thin Objects

A special unilateral NMR sensor has been designed for investigations of thin samples with a thickness of less than 1 mm and of surface effects of polymers. For use with the bar‐magnet NMR‐MOUSE®, the so‐called “crazy coil” is introduced with a low penetration depth. It is a flat meander coil etched on a printed circuit board with wiggles in the conductors. The design of the new coil and FEM simulations of the B ₁ field are presented. Different applications are discussed by means of illustrative examples. They are the detection of surface damage in rubber samples, the swelling and drying of a latex membrane exposed to cyclohexane vapor mimicking a chemical sensor, and the drying of a thin sprayed adhesive layer.

Bar‐magnet NMR‐MOUSE® with crazy coil.     

Peroxidase-catalyzed oxidation of β-carotene in HL-60 cells and in model systems: Involvement of phenoxyl radicals

Recent studies provide extensive evidence for the importance of carotenoids in protecting against oxidative stress associated with a number of diseases. In particular, reactions of carotenoids with phenoxyl radicals generated by peroxidasecatalyzed one-electron metabolism of phenolic compounds may represent an important antioxidant function of carotenoids. To further our understanding of the antioxidant mechanisms of carotenoids, we used in the present work two different phenolic compounds, phenol and a polar homologue of vitamin E (2,2,5,7,8-pentamethyl-6-hydroxychromane, PMC), as representatives of two different types of phenols to study reactions of their respective phenoxyl radicals with carotenoids in cells and in model systems. We found that phenoxyl radicals of PMC did not oxidize β-carotene in either HL-60 cells or in model systems with horseradish peroxidase (HRP)/H₂O₂. In contrast, the phenoxyl radicals generated from phenol (by native myeloperoxidase in HL-60 cells or HRP/H₂O₂ in model systems) effectively oxidized β-carotene and other carotenoids (canthaxanthin, lutein, lycopene). One-electron reduction of the phenoxyl radical by ascorbate (assayed by electron spin resonance-detectable formation of semidehydroascorbyl radicals) prevented HRP/H₂O₂-induced oxidation of β-carotene. PMC, but not phenol, protected β-carotene against oxidation induced by a lipid-soluble azo-initiator of peroxyl radicals. No adducts of peroxidase/phenol/H₂O₂-induced β-carotene oxidation intermediates with phenol were detected by high-performance liquid chromatography-mass spectrometry analysis of the reaction mixture. Since carotenoids are essential constituents of the antioxidant defenses in cells and biological fluids, their depletion through the reaction with phenoxyl radicals formed from endogenous, nutritional and environmental phenolics, as well as phenolic drugs, may be an important factor in the development of oxidative stress.     

Voltammetric and galvanostatic studies of hydrous and anhydrous iridium oxide films

Electrolytically grown hydrous oxide films on iridium wire electrodes have been thermally treated from 473 to 773 K. Anhydrous oxide films formed by this treatment have been subjected to cathodic polarization at the potential of the hydrogen evolution reaction, square-wave pulsing of potential from –0.25 to +1.25 V with respoect to SCE and to anodic galvanostatic polarization in 0.5 mol dm^–3 H₂SO₄. Cathodic pretreatment caused an increase of the voltammetric charge in the oxide formation region while the square-wave pulsing formed a hydrous oxide film whose voltammetric charge was superimposed on the charge of the anhydrous oxide film. Both procedures restored the hydrophilic nature of the electrode/solution interface. Potential-time curves during anodic galvanostatic polarization served as a diagnostic criterion for the stability and the state of the oxide film.     

Two-variable periodic perturbation of kinetic oscillations

Using one of the generic models (CO oxidation on Pt with surface-oxide formation) predicting kinetic oscillations in heterogeneous catalytic reactions, we show that the efficiency of two-variable periodic perturbations with respect to converting natural period-1 oscillations to period-l oscillations at the forcing frequency is remarkably sensitive to the kind of perturbations used. Counter-phase perturbations are much more effective compared to in-phase perturbations. The physics underlying these findings is suggestive of their applicability to many other models and/or real systems exhibiting kinetic oscillations.     

Influence of the Type and Method of Injection of Oxides Admixtures of Rare Earth Elements on Colour and other Properties of Dental Porcelain

A glassceramic material, which can be used in stomatology for production of dentinal layer of the dental crown multilayer coating, was received. In order to colour the material the admixtures of Tb and Ce compounds were used, as well as composite admixture representing a mixture of Ce, Nd and La oxides. It was demonstrated that the admixture of Tb oxide tones the material only when it is used together with Ce oxide. It was found that the more admixtures of rare earth elements oxides are contained in the sample composition, the higher the colour strength of the sintered material is. The wave length for the test samples is in the range of 600～650 nm, which corresponds to the yellow-orange and orange-red spectral range.     

Influence of Ionic Charge on Diffusion in the Surface Layer of Magnesia

The diffusion of ⁵⁷Co isotope on the MgO (100) surface was investigated by the edge-source method. The surface diffusion parameter, αD_sδ, where α is the segregation factor, D_s the surface diffusion coefficient, and δ the thickness of the high-diffusivity layer, was determined over the temperature region 750° to 1250°C. An Arrhenius plot shows a break at ∼1100°C. Below this temperature ionic or localized transport predominates and above it nonlocalized transport seems to predominate. The divalent Co ion diffuses faster than the trivalent Cr ion in the surface layer. The apparent activation energies for the localized surface diffusion of ⁵⁷Co and ⁵⁹Cr are 59±12 and 110±12 kj/mol, respectively.     

Low-temperature phase formation in the SrF2–LaF3 system

Phase formation in the SrF₂–LaF₃ system was studied at temperatures ranging from 300°C to 450°C using nitrate flux. The solubility of LaF₃ in SrF₂ decreases with decreasing temperature. The equilibrium width of the solid solution region Sr_1−xLa_xF_2+x at 400°C, it is 44.6 ± 0.4 mol% LaF₃ (x = 0.446), at 350°C — 38.3 ± 0.7 mol% LaF₃ (x = 0.383), and decreases almost to zero at 300°C.