Scanning tunnel microscope based on an ESO-03 Auger spectrometer and its application to studying highly dispersed carbon materials

A supervacuum scanning tunnel microscope (STM) based on an ESO-03 Auger spectrometer has been created. The design allows replacement of samples and STM needles and, if necessary, various modifications of the sample surface without violating the vacuum conditions. STM measurement conditions are indicated, and topographic data of highly dispersed carbon materials and pyrolytic graphite surface subjected to Ar⁺ bombardment are presented.Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 6, pp. 141–144, November–December, 1993.Translated by L. Chernomorskaya     

Separation of traces of heavy metals from an iron matrix by use of an emulsion liquid membrane

An emulsion liquid membrane method has been developed for separating traces of heavy metals from an iron matrix. A 1.0-mL volume of aqueous iron(III) solution (pH 2.0) was emulsified with a mixture of 0.6 mL toluene, 2.4 mL n -heptane, and 80 mg sorbitan monooleate (Span-80). The resulting water-in-oil type emulsion was gradually injected into 25 mL of 1.5 mol L^–1 hydrochloric acid solution containing 30 mmol L^–1 8-quinolinol and 1.0 mol L^–1 of ammonium sulfate and was dispersed as numerous tiny globules by stirring for 40 min. More than 90% of the iron(III) diffused through the oil layer to the external hydrochloric acid solution with the aid of complexation with 8-quinolinol, whereas trace heavy metals, e.g. Cr(III), Mn(II), Co(II), Ni(II), Cu(II), and Pb(II), remained quantitatively in the internal aqueous phase. After collecting the dispersed emulsion globules, they were demulsified and trace metals in the segregated aqueous phase were determined by graphite-furnace atomic absorption spectrometry. Owing to sufficient removal of the iron matrix trace metal impurities in high-purity iron were successfully determined without interference, as was confirmed by analysis of certified reference materials.     

Synthesis and characterization of PAni–SiO2 and PTh–SiO2 nanocomposites' thin films by plasma polymerization

In the present work, we explore the possibility to deposit polyaniline–silicon dioxide (PAni–SiO₂) and polythiophene–silicon dioxide (PTh–SiO₂) nanocomposites through a plasma polymerization route. The films were generated by spraying of mixtures of nano-sized silica particles dispersed in the liquid monomer into a plasma stream of the DC-plasma discharge reactor. The silica in the resulted polymer matrix changes the conduction mechanisms varying from ohmic to ballistic and traps inducing the space charged limited currents (SCLC). The silica modifies the morphology and composition of the deposited films.     

Calculation of long-range orientational order parameters in impure nematic liquid crystals using an extended van der Waals model

For the atended van der Waals model of a binary nematic system consisting of rigid biaxial molecules, we consider the following properties: the relation between the orientational order parameters of a nematic liquid crystal (NLC) S⁽¹⁾ and a nonmesomckphic impurity S⁽²⁾, the relation between S⁽²⁾ and the biaxiality parameter D⁽²⁾ of the impurity, and the lowered clearing temperature of NLC upon dissolution of the nonmesogen. The dependence of these characteristics on the fom and size of component molecules and the intermolecular attraction potential is analyzed. The model reproduces the experimental dependence of S⁽²⁾ and D⁽²⁾ on temperature and structure of the nematic matrix.Scientific Research Institute of Chemistry, St. Petersburg State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 5, pp. 106–115, September–October, 1993.Translated by L. Smolina     

Temperature dependence of electro-optical characteristics of polymer dispersed liquid crystal films

Polymer dispersed liquid crystal (PDLC) films consist of microdroplets of a liquid crystal dispersed in a polymer matrix. Their applications are based on the electrically controllable light scattering properties of the liquid crystal droplets. The effects of temperature on the electro-optical properties of PDLC films have been rarely investigated. In this work, we studied the light transmission on varying the temperature and frequency. It was observed that the transmission at a fixed voltage decreased with increasing temperature above 43°C, independent of frequency. We examined possible origins of this unusual dependence of the transmission on the temperature. It was concluded that conductivity effects due to free ions newly created at high temperatures could be responsible for the unusual behaviour observed.     

Temperature dependence of electro-optical characteristics of polymer dispersed liquid crystal films

Polymer dispersed liquid crystal (PDLC) films consist of microdroplets of a liquid crystal dispersed in a polymer matrix. Their applications are based on the electrically controllable light scattering properties of the liquid crystal droplets. The effects of temperature on the electro-optical properties of PDLC films have been rarely investigated. In this work, we studied the light transmission on varying the temperature and frequency. It was observed that the transmission at a fixed voltage decreased with increasing temperature above 43°C, independent of frequency. We examined possible origins of this unusual dependence of the transmission on the temperature. It was concluded that conductivity effects due to free ions newly created at high temperatures could be responsible for the unusual behaviour observed.     

“Guest-Host” effect in polymer-dispersed nematic liquid crystals

In this paper we report on a new optoelectronic material representing a polymer-dispersed liquid crystal (PDLC) film. This material exhibits optical response to the applied electrical field and is useful for displays and light gates. The effect of azo and anthraquinone dyes on the optical density of PDLC films has been studied. The proportion of the dye dissolved in an LC cell and the molar absorption coefficients were determined, and the influence of the dyes on the scattering efficiency of PDLC films was calculated.Institute of Theoretical and Applied Mechanics, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 6, pp. 114–117, November–December, 1993.Translated by L. Smolina     

The mechanism of formation of free-radical states upon the pulsed action of elastic waves on solid mixtures of donor-acceptor compounds

The action of a pulse of elastic waves on polycrystalline mixtures of donors and acceptors (for example, 3,6-di-tert-butylcatechol and 3,6-di-tert-butyl-1,2-benzoquinone with the addition of sulfur and polystyrene) results in the formation of monoradicals and radical pairs. The study of the products by ESR spectroscopy and X-ray analysis shows that the solid powder is dispersed to submicroscopic particles, including those of the mixed composition.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1192–1196, May, 1996.     

Measurement of the fluctuational grid parameters of molecular engagements upon the introduction of a highly dispersed mixture of Fe and FeO into a polymer

The Introduction of a highly dispersed mixture of Fe and FeO into amorphous-crystalline and amorphous polymers leads to microstructural changes, leading to an increase in the molecular engagement grid and change in the polymer properties. The most likely reason for the microstructural changes of the polymer compositions studied is a magnetic interaction of the iron and ferrous oxide particles with the polymer matrix.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1915–1917, August, 1990.     

Rheological properties of filled gels. Influence of filler matrix interaction

The dynamic moduli of gels filled with particles have been studied as a function of the volume fraction of dispersed particles _f (0–0.4) and of the way in which they interact with the gel matrix. Two gels of different nature were studied, viz. polyvinyl alcohol (PVA) — Congo red gels (a so-called rubber gel) and casein gels made by acidification of skimmed milk. Emulsion droplets stabilized by different macromolecules have been used as dispersed particles. If there was no interaction between the macromolecules adsorbed on the particles and the gel matrix, both the filled PVA and the filled casein gels showed a small decrease in the elastic moduli with _f , approaching the behaviour theoretically predicted for foams. In the case of interaction, the results for filled PVA gels roughly fitted the theoretical predictions, if the deformability of the emulsion droplets and the formation of an intermediate layer between the dispersed particles and the gel matrix was taken into account. The increase in the elastic moduli of the acid milk gels with _f was much greater than expected and was probably due to aggregation of the dispersed particles during gelation.     

Study of structural heterogeneity of HTSC Bi-ceramics

Using Bi-ceramics as an example, we estimate here the possibility of detemination of the structural heterogeneity of HTSC materials from X-ray powder diJjZaction data. me heterogeneity is due to the presence of alternating layers of different types within individual microcrystals. Explicit information on alternating fragments of diferent height is provided by the intensity distribution data of basal reflections, therefore we studied X-ray diffraction patterns of oriented specimens. The dipaction patterns from unidimensionally disordered structures were simulated based on a previously devised procedure for the calculation of dipaction profiles of mixed-layer minerals. The comparison of calculated and experimental dipaction patterns testifies that defects in the samples are really caused by the presence of layers of different heights corresponding to the 2212 phase built into the matrix of the basic 2223 phase. The concentration of such defects reaches 20% with a high segregation degree of both layer types.Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences. Geological Institute, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 5, pp. 133–146, September–October, 1993.Translated by T. Yudanova     

Thermodynamic behavior of adsorption systems with porous adsorbents along the curves describing equilibrium between bulk phases of an adsorptive

The thermodynamic aspects of adsorption equilibrium in systems with crystalline, liquid, and dense gas phases have been considered. The heats of phase transition and corresponding directions of mass transfer from the adsorbed phase into crystalline and liquid phases at different temperatures have been determined. The general equilibrium diagram in the coordinates Inp-T ^–1 has been given with indication of the equilibrium lines of three-phase systems and characteristic points on the isosteres of adsorption,viz., the Gurvitsch and quasicritical points.Deceased.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1480–1485, August, 1995.     

Morphology development in thermoplastic vulcanizates (TPV): Dispersion mechanisms of a pre-crosslinked EPDM phase

The fragmentation and dispersion in molten polypropylene (PP) of several pre-crosslinked and plasticized ethylene–propylene–diene terpolymer (EPDM) networks was studied. Thus, the morphologies and mechanical properties of PP/EPDM blends having similar compositions but made from either un-crosslinked, pre-crosslinked or dynamic-crosslinked EPDMs were compared. The results first highlight the importance of the gel fraction of the pre-crosslinked EPDMs, as well as the impact of the thermoplastic matrix proportion on the quality of the dispersion of such networks. As a result, pre-crosslinked EPDM having a gel fraction below g_EPDM = 0.7 can be finely and homogeneously fragmented and dispersed in presence of PP. It can be then admitted a collision–coalescence–separation type erosion mechanism of the EPDM domains. Nevertheless, contrarily to some theoretical model expectations, a partial fragmentation of the chemical networks was always observed even at very high crosslink density (g_EPDM > 0.7). Finally, the blends crosslinked under shearing (dynamic-crosslinked) showed a clear mechanical property synergy due to their fine and homogeneous morphology coupled with the full crosslinking of the elastomer. In the end, these results brought significant information on TPV morphology stabilization and their related mechanical properties.     

Initial magnetic susceptibility of ferrocolloids: The influence of chain aggregates

The behavior of a system of noninteracting chain aggregates of ferroparticles suspended in a liquid matrix and subjected to a weak uniform permanent magnetic field was studied based on the free energy functional of a monodisperse low-concentration magnetic colloid. The orientational response of a flexible chain to a weak external field showed that the model of rigid rods is applicable only for short chains (doublets and triplets) of large ferroparticles characterized by a strong magnetodipole interaction. The calculated values of the initial magnetic susceptibility of aggregated ferrofluid agree well with the computer simulation data.Translated from Kolloidnyi Zhurnal, Vol. 66, No. 6, 2004, pp. 756–765.Original Russian Text Copyright © 2004 by Ivanov.     

Oxidation of Methanol on Pt,Pt–Ru,and Pt–Ru–Mo Electrocatalysts Dispersed in Polyaniline: An in situ Infrared Reflectance Spectroscopy Study

The electrochemical oxidation of methanol was investigated on a Pt–Ru–Mo catalyst with an in situ infrared reflectance spectroscopy. The electrocatalysts were prepared by an electrochemical deposition and dispersed in a conducting three-dimensional matrix of polyaniline (PAni). We observed that CO₂ is produced from methanol oxidation at 350 mV vs. RHE on PAni/Pt–Ru–Mo, which is 100 mV less negative than on PAni/Pt–Ru and 200 mV less than on PAni/Pt. The results suggest that Pt–Ru–Mo is less sensitive to CO_ADS poisoning than Pt–Ru and much more sensitive than Pt. Large differences are observed concerning the average wavenumber of _ADS between Pt–Ru–Mo, Pt–Ru, and Pt.     

Reversed-phase high-performance liquid chromatography of protamines

The protamines from the gonads of the sturgeonAcipenser stellatus have been separated by high-performance liquid chromatography. The proteins were eluted with mixtures of water and ethanol having a gradient of ethanol concentrations in the presence of trifluoroacetic acid (TFA). The influence of the concentration of TFA and the temperature of the column on separation was studied. The quantitative (95–98%) isolation of the protamines from the column was achieved at a temperature of 30°C and a 0.15% concentration of TFA.Moscow Technological Institute of the Meat and Dairy Industry. Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 744–748, November–December, 1986.     

Soliton mechanism of ion mobility in incommensurate structures

A model of soliton ion mobility in one-dimensional incommensurate structures is considered as the possible mechanism of information transmission in molecular systems. Numerical calculations of the dependence of the diffusion activation energy on the concentration of mobile ions are performed. Experimental NMR data on lithium ion mobility in a model Li_xNbSe₃ (0Zhurnal Strukturnoi Khimii, Vol. 34, No. 6, pp. 135–140, November–December, 1993.Translated by L. Chernomorskaya     

PVC matrix membrane electrodes based on cobalt and nickel phenanthroline complexes for selective determination of cobalt(II) and nickel(II) ions

Potentiometric sensors for determining cobalt and nickel ions are described. They are based on the use of cobalt and nickel tris(1,10-phenanthroline)-TPB as electroactive compounds dispersed in plasticized poly(vinyl chloride) matrix. The sensors exhibit fast, near-Nernstian responses for cobalt and nickel-phenanthroline cations over the pH range 3–11 with a slope of 30.3 ± 0.3 mV/concentration decade. In the presence of excess 1,10-phenanthroline reagent, cobalt(II) and nickel(II) ions at concentration levels as low as 4 × 10^–6 M are accurately determined. The results show an average metal ion recovery of 98.5% with a mean standard deviation of 0.5%. Cobalt in organometallic compounds and nickel in silicate rocks are determined by these sensors and results agreeing fairly well with atomic absorption spectrometry are obtained.     

IR-spectral study of the metal state in low-percentage alumina-rhenium and alumina-technethillm catalysts following high-temperature reductive treatment

The state of Re and Tc in low-percentage alumina-rhenium (0.25 % Re) and aluminatechnetium (0.1 % Tc) catalysts reduced by H₂ at 500–900 °C was studied using IR spectra of the diffuse reflection of the adsorbed CO. A highly dispersed (probably two-dimensional) metal phase with a lowered electron-donating ability due to strong metal—support interaction is present on the surface of these catalysts along with the ionic forms of Re and Tc at +1 and +4 oxidation states. CO adsorbed on such metals in a linear form can be removed by evacuation even at 20°C. The amount of highly dispersed metal phase on the support surface increases monotonically with an increase in the activation temperature of Re/Al₂O₃ and Tc/Al₂O₃. The activity of the catalysts in the dehydrogenation ofn-dodecane varies directly with the concentration of the electron-deficient highly dispersed metal phase. It is therefore concluded that highly dispersed Re⁰ and Tc⁰ formed during high-temperature treatment by H₂ are the precursors of the catalytically active centers in the paraffin dehydrogenation reaction.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 664–667, April, 1993.     

Transient processes of diffusion-controlled quenching of pyrene fluorescence on the surface of SiO2

Using the diffusion-controlled bimolecular reaction of quenching of pyrene fluorescence by N,N-dimethylaniline on the surface of thermally activated highly dispersed SiO₂ as an example it is shown that a transient non-steady-state process is observed in the initial section of the kinetics.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 30, No. 6, pp. 328–331, November–December, 1994.