Gradient structure of polypropylene composites filled with carbon black

Russian Chemical Bulletin - Gradient polymer composites were prepared by melt-mixing of carbon black and polypropylene in a compounder and subsequent hot pressing of pellets. The thermally treated...     

Ductile-to-ductile transition in dispersely filled composites based on thermoplastic polymers

The fracture mechanism for rubber-filled composites based on gutta-percha, LDPE, medium-density PE, and rubber particles has been studied. An increase in the concentration of filler particles leads to a change in the stress-strain behavior of the composites from neck propagation to homogeneous plastic deformation. For the filled composites, the criterion for the ductile-to-ductile transition is the equality of yield and draw stresses. The critical concentration of rubber particles at the ductile-to-ductile transition is controlled by the ratio between the yield stress of matrix polymer and the neck propagation stress. Transition from neck propagation to homogeneous plastic flow of the material is accomplished under two conditions: the breaking strength of the polymer matrix should be higher than the yield stress, and stretching of the composite should not be accompanied by the formation of diamond cracks. The latter condition is fulfilled when the dimensions of rubber particles are below a certain critical value, which is determined by the ductility of the matrix.     

Structure inhomogeneities of medium-range order in fluorozirconate glasses

Images of cleaved surfaces were obtained for 53ZrF₄-20BaF₂-4LaF₃-3AlF₃-20NaF (ZBLAN) glasses and fused quartz using an NTMDT atomic force microscope. It is shown that the scatter of particle size depends on the cooling rate and is 21–48.5 Å for the cleaved surface of ZBLAN glass obtained by very fast cooling and 68–172 Å for the cleaved surface of ZBLAN after slow cooling. For cleaved fused quartz, the range is 25-18 Å.     

Relationship of intensities of absorption bands of adsorbed molecules to the energy of adsorption and the number of adsorption sites

A derivation of an equation which makes it possible to relate the intensities of the absorption bands in the optical spectra of test molecules adsorbed on a surface to the number and energetics of the adsorption sites has been proposed. In the general case, the ratio between the intensities of absorption bands is determined by the energy of the interaction of the adsorbate with the surface sites, the ratio between the numbers of sites, and the oscillator strengths of the optical transitions of the adsorbed molecules. The validity of the equation has been confirmed by analyzing the transmission spectra of p-dimethylaminoazobenzene adsorbed on monosubstituted forms of Glukhov kaolinite containing singly (Na⁺, H⁺), doubly (Mg²⁺), and triply (A1³⁺) charged cations in its exchangeable positions.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 4, pp. 475–480, July–August, 1985.     

Ionic Mobility, Phase Transitions, and Superionic Conduction in Solid Solutions (100 ? x)PbF2-xZrF4 and Crystals K2ZrF6, (NH4)2ZrF6, KSnZrF7, and M(NH4)6Zr4F23 (M = Li, Na)

Methods of (¹⁹F, ¹H) NMR and impedance spectroscopy are used to investigate the internal mobility and ionic conduction in solid solutions arising in the system PbF₂-ZrF₄ and polycrystals KSnZrF₇, Li(Na)(NH₄)₆Zr₄F₂₃, and M₂ZrF₆ (M = K, NH₄). Factors responsible for the form of ionic motions and their energetics at 170–550 K are considered. It is established that the phase transitions in these compounds are connected with the crystal transition to a superionic state and that the high ionic (superionic) conductivity of beta phases is due to the diffusion of fluoride ions, ammonium cations, and possibly alkali metal cations. The obtained data testify to a substantial role of chainlike aggregation of anionic groupings and a variableness of structural mechanisms of formation of such chains in fluorozirconates for the development of translational diffusion in these compounds.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 573–582.Original Russian Text Copyright © 2005 by Kavun, Uvarov, Slobodyuk, Goncharuk, Kotenkov, Tkachenko, Gerasimenko, Sergienko.     

Electron-electron correlations in Raman spectra of VO2

Physics of the Solid State - It has been shown that, in single crystals and films of a strongly correlated material, namely, vanadium dioxide, upon a thermally stimulated phase transition from the...     

Aggregation of clay platelets in nematic liquid crystal, 5CB: microstructure,electrical conductivity and rheological investigations

The microstructure, electrical conductivity and rheological properties of a nematic liquid crystal (5CB) doped at concentrations up to 4.5 wt% of montmorillonite (MMT) or organomontmorillonite (OMMT) clay nanoplatelets, were investigated at temperatures between 293 and 310 K. Microscopy and electrical conductivity assessment revealed noticeable differences in aggregation in MMT and OMMT suspensions, MMT nanoplatelets showing a strong tendency to aggregation. The incubation of 5CB in the presence of MMT initially produced loose aggregation, followed by the formation of compact aggregates. The latter had practically no influence on the surrounding inter-aggregate regions. In the case of OMMT, a greater degree of integration of the nanoplatelets was observed within the liquid crystal structure of 5CB, resulting in a noticeable effect on electrical conductivity and activation energy of the composite material. Thixotropy was observed in suspensions of 5CB composites formed with either MMT or OMMT. A composite of 5CB with OMMT also exhibited anomalous viscous thinning at shear rates below 100 s^?1. A structural model is suggested to explain this behaviour.     

Synthesis and Structure of Tin(II) Hexafluorozirconate

The crystal structure of SnZrF₆ is determined. The compound is synthesized by slow crystallization from a melted mixture of SnF₂ and ZrF₄ (2 : 1). The crystals are monoclinic: a = 6.6119(5), b = 5.2503(5), c = 6.9929(6) Å, = 114.239(4)°, space group P2/n, Z = 2. The structure is layered. The layers are formed from the chains of edge-sharing, eight-vertex zirconium polyhedra and Sn²⁺ cations. The Zr–F and Sn–F bond lengths in the layer vary from 2.309(1) to 2.269(1) Å and from 2.186(1) to 2.361(1) Å, respectively. The layers are linked by intermolecular Sn–F bonds with lengths of 2.868(1) and 2.871(1) Å.     

Electron spectra of Hammett dye-indicators sorbed by montmorillonite

Theoretical and Experimental Chemistry -