Physicochemical aspects of the creation of modern light-sensitive materials based on polymethine dyes

Features of the photophysical and photochemical characteristics of polymethine dyes that determine their use as light-sensitive materials (luminescent light concentrators, fluorescent probes and markers for the intercalation of DNA, laser media, polymerization photoinitiators, electroluminescent media) are analyzed. The main paths of the degradation of the electronic excitation energy (photoisomerization, intercombination and internal conversion, electron phototransfer in ion pairs, interaction of chromophores, like and mixed association) are discussed. The relation between these factors and the structure of the dyes and the nature of the medium is examined. Special attention is paid to methods of creating and optimizing colored light-sensitive polymeric materials. Institute of Organic Chemistry, National Academy of Sciences of Ukraine, 5 Murmanskaya ul., Kiev 253094. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 34, No. 4, pp. 214–232, July–August, 1998.     

Physicochemical principles for developing new materials based on silicate dispersed minerals

We consider the physicochemical principles for obtaining effective new sorbents, catalysts, supports, and fillers made from natural dispersed minerals using heat treatment, modification by inorganic and organic compounds, stratification of carbon layers, introduction of inorganic and organic oligomers and polymers into the structure of the minerals. We discuss the properties and practical use of the new materials.     

Some new methods for the determination of rare-earth elements in geological materials using thermal and epithermal neutron activation

Three procedures are outlined for the determination of rare-earth elements in geological materials. The irradiation of the samples is carried out by either thermal or epithermal neutrons. Two of the methods, one of which is especially suitable for ultramafic rocks are based on radiochemical separations, while in the third method non-destructive analysis is applied to apatites. The γ-ray activity measurements are performed by means of coaxial Ge(Li)-detectors.     

Synthesis and properties of chromium-containing bismuth titanates with the pyrochlore structure

Chromium-containing bismuth titanates with the pyrochlore-type structure Bi_1.6Cr _x Ti₂O_6.4+1.5x were synthesized by the ceramic method. The region of formation of solid solutions of pyrochlores (chromium-doped bismuth titanates) was determined. The picnometric and X-ray densities were compared, and the electrophysical and magnetic characteristics were studied.     

Physicochemical problems encountered in the development of oxygen-conducting oxide materials for new devices for chemical energy conversion

The data on the properties of ion- and mixed-conducting oxides promising for the development of new membrane materials for processing natural gases and solid-oxide fuel cells with low working temperatures (<800 K) are presented. Advantages of using perovskite-type oxides based on hetero-substituted lanthanum gallate for the development of materials for oxygen-selective electrolytes and electrodes are substantiated. The most promising methods for the production of low-defect thin-film structures providing the efficient conversion of the hydrocarbon fuel energy are considered. Dedicated to the 90th anniversary of the L. Ya. Karpov Institute of Physical Chemistry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1106–1117, June, 2008.     

Physicochemical properties of electrode materials based on substituted yttrium manganite

Electrode materials Y_0.5Ca_0.5Mn_1–x (Co,Ni)_xO₃(x = 0–0.1) have an o-orthorhombic perovskite structure. Doping with transition metals raises the content of ions Mn⁴⁺ from 49% at x = 0 to 62% at x = 0.05 Ni. At 500–650 K there takes place an o-o-orthorhombic transition, with the thermal expansion coefficient rising from (7.1–8.1) × 10^–6 to (10.5–11) × 10^–6 K^–1. Composition Y_0.5Ca_0.5Mn_1–x (Co, Ni)_xO₃ is n-type semiconductor with a considerable oxygen constituent at >1000 K. Effect of the electrode material composition on the resistance parameter (/d) of an intermediate layer E/SE and on the polarization resistance (R ) of the triple-phase boundary E/SE/GP is similar. At 300–1100 K and 10²–10⁵ Pa, minimum values of these quantities are exhibited by samples with the Y_0.5Ca_0.5Mn_0.95Ni_0.05O₃ electrode layer 50 mg cm^–2 thick.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 291–297.Original Russian Text Copyright © 2005 by Tikhonova, Poluyan, Glushko, Vecher, Znosok.     

Determination of the rare-earth elements in geological materials by thin-film X-ray fluorescence and inductively-coupled plasma atomic-emission spectrometry

Thin-film XRF and ICP-AES analytical procedures for the determination of the rare-earth elements (REE) in rocks, involving preconcentration by ion-exchange and co-precipitation with Fe(OH)(3) for thin-film preparation, and matrix modification, are described. The REE in five international reference rocks have been determined, with correction for spectral line overlap whenever necessary. The results obtained by using X-ray fluorescence spectrometry compare well with those of inductively-coupled plasma atomic-emission spectrometry, and with other values reported in the literature.     

Synthesis and properties of Sc- and Mg-doped bismuth titanates with the pyrochlore structure

Scandium(Magnesium)-containing bismuth titanates with the pyrochlore structure have been synthesized for the first time. Their homogeneity range has been determined by means of X-ray diffraction analysis and scanning electronic microscopy. Scandium and magnesium distribution over the cationic positions has been studied. Electrophysical properties of single-phase compounds have been studied. The total conductivity of the compounds is a function of magnesium (scandium) and bismuth concentrations.     

New polymer materials with controlled nanoporous structure based on N-vinylpyrrolidone

The polymer networks with nanoporous structure were obtained by the crosslinking free-radical copolymerization of N-vinylpyrrolidone with triethylene glycol dimethacrylate in bulk in the presence of amphiphilic copolymer and its fractions as templates. The templating agents consisted of copolymer or their fragments with similar monomer units and different molecular weight. Macromolecular templates were shown to be removed from the polymer composite by PrⁱOH leaving the pores. The values of the specific surface areas, the total pore volumes, pore size, and pore size distribution were measured by the method of low-temperature nitrogen absorption. The maximum value of the specific surface area was calculated to be ~26 m² g^–1. The value was significantly higher than that for the usual copolymer network. The relationship between specific surface area, parameters of pores, and macromolecular structure of template has been established. It is shown by Brunauer—Emmett—Teller method that the macromolecules having a branched architecture are more effective for the preparation of the polymer network with more developed specific surface area and narrow pore size distribution.

     

Polymeric materials based on main group elements: the recent development of ambient temperature and controlled routes to polyphosphazenes

This Perspective discusses the development of new routes to polyphosphazenes, [R(2)P[double bond, length as m-dash]N](n), that occur at ambient temperature and, in some cases, allow molecular weight control and access to narrow molecular weight distributions and block copolymers. For example, the room temperature silyl-carborane initiated ring-opening polymerisation of (NPCl(2))(3) is described together with chain growth condensation polymerisations of phosphoranimines Cl(3)P[double bond, length as m-dash]NSiMe(3) and BrMePhP[double bond, length as m-dash]NSiMe(3). Recent works on donor-stabilised cationic phosphoranimines are also discussed.     

Prediction of transport properties of new functional materials based on lanthanum-strontium cuprates: Molecular mechanics calculations

The method of molecular dynamics is used for prediction of properties of new functional materials based on lanthanum-strontium cuprates La_{2 ? x} Sr _x CuO_{4 ? δ} as new materials of the solid state ionics. The most interesting phases are synthesized to test the obtained calculation data and their electrophysical and thermomechanical characteristics are studied. It is shown that the high values of the oxygen diffusion coefficients are obtained in the La_{2 ? x} Sr _x CuO_{4 ? δ} solid solutions with a high replacement degree of Sr → La (up to x = 1). The calculated values of lattice cell parameters, thermal expansion coefficients and oxygen diffusion coefficients agree with the experimental data. The observed anisotropy of anionic transport for all the studied compositions corresponds to the regularities of crystal structure of complex oxides. Using the molecular dynamics method allows tracing the contribution of separate types of oxygen ions (equatorial and apical) into ionic transport at the microscopic level and also confirming directly that oxygen diffusion occurs according to the usual jump mechanism, mainly in (CuO₂) layers.     

Separation and preconcentration of the rare-earth elements and yttrium from geological materials by ion-exchange and sequential acid elution

The abundance of rare-earth elements (REE) and yttrium in geological materials is generally low, and most samples contain elements that interfere in the determination of the REE and Y, so a separation and/or preconcentration step is often necessary. This is often achieved by ion-exchange chromatography with either nitric or hydrochloric acid. It is advantageous, however, to use both acids sequentially. The final solution thus obtained contains only the REE and Y, with minor amounts of Al, Ba, Ca, Sc, Sr and Ti. Elements that potentially interfere, such as Be, Co, Cr, Fe, Mn, Th, U, V and Zr, are virtually eliminated. Inductively-coupled argon plasma atomic-emission spectroscopy can then be used for a final precise and accurate measurement. The method can also be used with other instrumental methods of analysis.     

Soils of Azores islands: elemental characterization with an emphasis on rare-earth elements

This work addresses the chemical features of topsoils from Pico, São Jorge and São Miguel islands (Azores, Portugal), resulting from the weathering of more or less recent volcanic materials, namely pyroclastic debris, scoriae and basaltic rocks. The fractions under 64 μm of the surface-soil samples (0–10 cm) were put through k ₀-standardized, instrumental neutron activation analysis (k ₀-INAA), and their contents in 29 chemical elements were determined. Overall, the results show the chemical composition in the top horizon of soils to be correlated with the type of initial material, as well as with the age of formation of the island. The more relevant differences between the surveyed islands are: (1) a positive Ce anomaly in soils from São Miguel, most probably due to the higher age of that island; and (2) a fractionation between heavy and light rare-earth elements (REEs) in São Miguel, not found in the younger Pico and São Jorge. Other than the islands’ age, terrain altitude seems another relevant factor in differentiating the topsoils’ composition.     

Synthesis of new materials based on polythiophenes substituted with mesogen groups

A new family of conjugated polymers formed by 3-alkyloximethylthiophenes substituted with a biphenyl group was synthesised by a route involving first the coupling of a functionalised alkyl chain, from 8 to 12 carbon atoms, to 3-methanolthiophene, and then the attachment of the mesogen group. The monomer was characterised by conventional techniques, and thermal studies were also achieved. The polymerisation of these units was carried out via oxidative polymerisation with FeCl₃. The resultant polymers were characterised by FT-IR, elemental microanalysis and XPS. Subsequently, these materials were doped with I₂ and characterised by the above techniques and conductivity measurements, which indicated that these materials are in the semiconductor range. The polymerisation of these monomers was also carried out via electrochemical methods, and it was found that, together with the oxidation of the thiophene ring, the oxidation of the biphenyl group is also produced, for which an over-oxidised material is obtained, as demonstrated by XPS analysis and theoretical calculations.     

Physicochemical properties of composite sorption-active materials based on zeolite and fluorinated ethylene derivatives

A procedure was suggested for preparing composite sorption-active materials based on zeolite and fluorinated ethylene polymers. The morphology of these materials, their resistance to mechanical action, and their ability to sorb water vapor under static and dynamic conditions were examined.