TSDC spectroscopy of relaxational and interfacial phenomena

Applications of thermally stimulated depolarisation current (TSDC) technique to a variety of systems with different dispersion phases such as disperse and porous metal oxides, polymers, liquid crystals, amorphous and crystalline solids, composites, solid solutions, biomacromolecules, cells, tissues, etc. in gaseous or liquid dispersion media are analysed. The effects of dipolar, direct current (dc) and space charge relaxations are linked to the temperature dependent mobility of molecules, their fragments, protons, anions, and electrons and depend on thermal treatment, temperature and field intensity of polarisation, heating rate on depolarisation or cooling rate on polarisation. Features of the relaxation mechanisms are affected not only by the mentioned factors but also by morphological, structural and chemical characteristics of materials. The interfacial phenomena, especially the role of interfacial water, received significant attention on analysis of the TSDC data. Comparison of the data of TSDC and dielectric relaxation spectroscopy (DRS), differential scanning calorimetry (DSC), 1H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial water, adsorption/desorption of nitrogen, water and dissolved organics demonstrates high sensitivity and information content of the TSDC technique, allowing a deeper understanding of interfacial phenomena.     

Ionic mobility and structure of glasses in Zrf<Subscript>4</Subscript>—Bif<Subscript>3</Subscript>—Mf<Subscript>2</Subscript> (M = Sr,Ba, Pb) systems according to Nmr,Ir, and Raman spectroscopic data

The NMR (¹⁹F and MAS NMR ¹⁹F), IR, and Raman spectroscopic methods are used to study the ionic mobility and structure of a series of new glasses in ZrF₄—BiF₃—MF₂ (M = Sr, Ba, Pb) systems in a temperature range of 180 K to 500 K. The temperature range, in which diffusion of fluorine ions becomes the dominant form of ionic motion, is determined by the nature of the M₂+ cation. The factors determining the basic model of the structure of glasses in ZrF₄—BiF₃—MF₂ (M = Sr, Ba, Pb) systems and conditions under which bismuth polyhedra can participate in the construction of the glass network are considered. According to the data of impedance spectroscopy, the studied glasses have relatively high ionic conductivity (δ ≥ 10–₄ S/cm above 480 K).     

Fracture of composites based on polyethylene and elastic particles

The composites based on low-density polyethylene with elastomer filling particles are studied. A fracture mechanism induced by the fracture of filler particles or their separation from the matrix polymer is revealed. The fracture of the composites is caused by the growth of formed rhombic pores. The natural relative elongation in a neck is shown to be an important characteristic of a polymer. If the relative elongation in a neck is lower than the strain of appearance of rhombic pores, they form at the stage of uniform tension after necking, and the composite remains plastic. If the relative elongation in a neck is higher than the strain of formation of rhombic pores, they nucleate during necking, and the material undergoes quasi-brittle fracture. Good adhesion between the matrix polymer and elastic particles hinders the appearance of rhombic pores in a neck and, thus, retains high deformation properties of the composites.     

Rotation numbers and moduli of elliptic curves

Given a circle diffeomorphism f, we can construct a map taking each real number a to the rotation number of the diffeomorphism f +a. In 1978, V. I. Arnold suggested a complex analog To this map. Given a complex number z with Im z > 0, Arnold used the map f + z to construct an elliptic curve. The moduli map takes every number z to the modulus μ(z) of this elliptic curve.     

The effect of filler content on the lower yield stress of polymer composites

The effect of the concentration of the dispersed elastic filler on the lower yield stress of matrix composites based on plastic polymers is studied. As the matrix polymers, LDPE-HDPE and LDPE-(medium-density PE) are used. The elastic filler is rubber crumb prepared by roll grinding of worn tires or by deformation grinding of ethylene-propylene-diene rubber. Irrespective of the type of filler particles and their adhesion to the polymer matrix, the lower yield stress σ_d of the composite is described by the linear law σ_d = σ_dm(1 ? V _f ), where σ_dm is the lower yield stress of the polymer matrix and V _f is the volume content of the filler. Analysis of the published data shows that this relationship is quite general and describes the effect of rigid inorganic particles on the lower yield stress when adhesion between the filler particles and the matrix is poor.     

Relaxation phenomena in poly(vinyl alcohol)/fumed silica affected by interfacial water

Interaction of poly(vinyl alcohol) (PVA) with fumed silica was investigated in the gas phase and aqueous media using adsorption, broadband dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization current (TSDC), infrared spectroscopy, thermal analysis, and one-pass temperature-programmed desorption (OPTPD) mass-spectrometry (MS) methods. PVA monolayer formation leads to certain textural changes in the system (after suspension and drying) because of strong hydrogen bonding of the polymer molecules to silica nanoparticles preventing strong interaction between silica particles themselves. This strong interaction promotes associative desorption of water molecules at lower temperatures than in the case of silica alone. Interaction of PVA with silica and residual water leads to depression of glass transition temperature (T(g)). There are three types of dipolar relaxations at temperatures lower and higher than the T(g) value. A small amount of adsorbed water leads to significant conductivity with elevating temperature.     

Influence of the conditions of photooxidation of natural water on the yield of carbonyl compounds

The yield of carbonyl compounds in treatment of river water and model solutions of humic acid as a function of the ozone uptake and conditions of UV irradiation was analyzed.     

Relationship between kinetic and thermodynamic characteristics of alumosilicate catalysts

The kinetics of cumene dealkylation over alumosilicate catalysts of different nature has been investigated and the calculated thermodynamic adsorption heats of cumene and benzene are given. It is shown that the adsorption heats of cumene and benzene do not depend on the temperature or surface coverage in the region under study. A correlation between the activation energies and the adsorption heats of reaction components is observed.

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