Raman study of PANI thin film during long time period in dependence on storage conditions

Conducting polymer polyaniline which is nowadays in forefront of the interest was in our study prepared in a form of thin films from anilinium sulfate by its chemical oxidation using ammonium peroxydisulfate. During the oxidation process, the polyaniline was deposited on glass slides and immersed into reaction mixture. Two sets of polyaniline thin films were prepared with different oxidation times (10, 20, 30, and 40 min). The first set was kept dry in desiccator and the second one was freely exposed to air moisture. Raman spectroscopy, nondestructive technique which is very sensitive to changes in structure of polymers, was used for the characterization of the protonation state of prepared polyaniline thin films. It was found that storage conditions affect the protonation state which in case of samples kept in desiccator is maintained without significant changes for longer time. Raman spectroscopy also revealed the dependence of protonation state on the oxidation time and 10 min proved as not sufficient for the creation of the protonation form of polyaniline.     

Determination of mechanical properties by instrumented indentation

The paper reviews the current state of the depth-sensing indentation (sometimes called nanoindentation), where the information on material behaviour and properties is obtained from the indenter load and depth, measured continuously during loading and unloading. It is shown how the contact parameters and principal characteristics are determined using pointed or spherical indenters. Indentation tests can be used for the measurement of hardness and elastic modulus, and also of the yield stress and for the construction of stress–strain diagrams, for the determination of the work of indentation and its components. Most devices use monotonic loading and unloading, but some also enable measurement under a small harmonic signal added to the basic monotonously increasing load. This makes possible continuous measurement of contact stiffness and the study of dynamic properties and the determination of properties of coatings. One section is devoted to the measurement on viscoelastic-plastic materials, where the delayed deforming must be considered during the measurement as well as in data evaluation. Instrumented indentation can also be used for the study of creep under high temperatures. The paper also discusses the errors arising in depth-sensing measurements and informs briefly about some other possibilities of the method.     

Inhomogeneous inverse problem in finite elasticity

For a class of materials for which the principal strain directions always coincide with the principal stress directions one can determine the stress field in an inhomogeneously deformed body from given boundary conditions and a known strain field without knowing the constitutive equations. Each point of the inhomogeneously deformed body contains information such as that derived from an individual homogeneous identification test. The practically important two-dimensional case leads to a problem of solving a linear hyperbolic system where two differential equations describe the principal stress components. The problem can be reduced to that of integration along characteristics.Under a certain globality condition the existence, uniqueness, and correctness of the solution are guaranteed in the whole test piece. It is shown that the globality condition is closely related to whether or not the test piece is isotropic and elastic. The influence of experimental error on the correctness of problem formulation is discussed.

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Abstrakte Für die Klasse der Materialen, für welche die Grundspannungsrichtungen und die Grundverformungsrichtungen gleich sind, kann man das Spannungsfeld in einem inhomogen deformierten Körper für gegebene Randbedingungen und einem bekannten Verformungsfeld ohne Kenntnis der detailierten Form der Dehnungs-Spannungsgleichung bestimmen. Jeder Punkt des inhomogen deformierten Körpers liefert dieselbe Information wie ein individueller homogener Test. Der praktisch wichtige zweidimensionale Fall führt zu einem Problem der Lösung eines linear hyperbolischen Systems von zwei Differentialgleichungen für die Grundspannungskomponenten. Das Problem kann auf die Integration entlang der Charakteristik des Systems reduziert werden.Unter einer Bedingung der Globalität das die Existent, Eindeutigkeit und Richtigkeit der Lösung in der ganzen Testprobe gewährleistet sind. Es wird gezeigt, dass diese Globalitätsbedingung damit zusammenhängt eng, ob die Testprobe isotrop und elastisch ist. Der Einfluss der experimentellen Fehler auf die Richtigkeit der Formulation des Problems wird auch analysiert.

     

Rheological behaviour of two-phase flow of solid particles in a gas

The present investigation was concerned with the rheological behaviour of dilute suspensions of solid particles in a gas in a vertical cocurrent flow moving upwards. Starting from the experimentally determined dependence of the pressure drop on the concentration of solid particles and the Reynolds number of the carrier medium in the steady flow region, the rheological parameters were estimated using pseudo-shear diagrams. Air was the carrier medium and the dispersed phase was one of six fractions of polypropylene powder and five fractions of glass ballotini. The results show that the investigated two-phase systems have pseudoplastic character which becomes more pronounced with increases in concentration, equivalent diameter and density of solid particles in the flowing suspension. C _d coefficient of particle resistance - d _e equivalent diameter of particles - D column diameter - Fr Froude number - g gravitational acceleration - K rheological parameter - L length - n rheological parameter - p _t pressure drop due to friction - p _m total pressure drop - p _ag pressure drop due to acceleration of the gas phase - p _as pressure drop due to acceleration of the solid phase - p _g hydrostatic pressure of the gas phase - p _s specific effective weight of the dispersed phase - r radius - Re Reynolds number - Re _p Reynolds number of a particle - Re _G generalized Reynolds number - Re _G1 generalized Reynolds number relating to the end of the laminar flow region - Re _G2 generalized Reynolds number relating to the beginning of the turbulent flow region - w _z axial component of velocity - u _t steady free-fall velocity of a single particle - w average velocity - w _g average velocity of the gas phase - w _s average velocity of the dispersed phase of solid particles - relative mass fraction of solid particles - x _s volume fraction of solid particles - _g coefficient of pressure drop due to friction - µ dynamic viscosity - _g density of the gas phase - _m density of the suspension - _s density of solid particles - _ds density of the dispersed phase - _w shear stress at the wall     

Preparation,spectroscopic and magnetic characterization of Cu(cyclam)M(CN)<Subscript>4</Subscript> complexes exhibiting one-dimensional crystal structures (cyclam = 1,4,8,11-tetraazacyclotetradecane,M = Ni,Pd, Pt)

From the systems Cu(II)–cyclam–[M(CN)₄]^2? (cyclam = 1,4,8,11-tetraazacyclotetradecane; M = Ni, Pd, Pt), three cyanidocomplexes Cu(cyclam)M(CN)₄ [M = Ni (1), Pd (2), Pt (3)] were isolated and characterized by chemical analysis, IR and UV–VIS spectroscopy. The three compounds are isostructural, and their crystal structures are formed by quasi-linear chains exhibiting [–Cu(cyclam)–μ–NC–M(CN)₂–μ–CN–]_n composition. The Cu(II) atoms reside on centres of symmetry and are coordinated in the form of an elongated octahedron with mean equatorial Cu–N bonds of 2.015(12), 2.017(13) and 2.011(11) Å in (1), (2) and (3), respectively, and weakly N-bonded bridging cyanido ligands in the axial positions [2.5321(9) Å in (1), 2.518(2) Å in (2) and 2.549(3) Å in (3)]. Hydrogen bonds of the N–H···N_cyanido···H–N type link neighbouring chains, and a topologically square network of paramagnetic Cu(II) atoms is formed. The magnetic susceptibilities of all three complexes follow the Curie-Weiss law with a weak antiferromagnetic exchange coupling below 5 K.     

Low-density polyethylene in mixtures of hexane and benzene derivates

Preferential sorption, equilibrium swelling degree, and volume of the swollen membrane in systems low-density polyethylene + hexane + aromatic compound (benzene, methylbenzene, or ethylbenzene) were studied using gravimetric and dilatometric methods at the temperature of 25 °C. Aromatic compounds are preferentially sorbed in low-density polyethylene compared to hexane. Experimental volume changes of the membrane were found to be noticeably different from those calculated on the basis of mass sorption data under the assumption of additivity. This difference points to the existence of the interactions between the polymer and the surrounding liquid mixture. The volume swelling degree curves are close to each other in the whole concentration range of the binary liquid mixture (hexane + aromatics) suggesting that the attractive forces between the polymer chains are the deciding factor limiting the volume expansion of the membrane in all three systems to the same extent.     

Mechanical properties of silica hydrogels prepared and aged at physiological conditions: testing in the compression mode

The mechanical properties for silica hydrogel prepared at physiological conditions are reported in this paper. The mechanical testing was performed in the compression mode determining the mechanical characteristics as a function of aging time in TRIS buffer up to 14 days. In addition to a typically used gradient method for Young’s modulus determination from the stress–strain curves, a new phenomenological model was proposed to describe the experimental data. The mechanical properties were stabilized after 2 days of aging, which was concluded from an increase in Young’s modulus between 90 and 400 kPa, an increase in stress at break between 50 and 100 kPa and by a decrease in relative deformation at break from 0.26 to 0.16. The height of samples was constant in the first three days of aging followed by a decrease by ~20%. Dissolving of silica hydrogel characterized through determination of silica content in TRIS buffer employing the molybdenum method was not found to be responsible for this phenomenon. The phenomenological model is proposed to be used for a reliable evaluation of mechanical properties of silica as well as other hydrogels exhibiting low Young’s modulus.     

Rapid qualitative and quantitative ultra high performance liquid chromatography method for simultaneous analysis of twenty nine common phenolic compounds of various structures

Twenty nine phenolic compounds comprising nine phenolic acids, sixteen flavonoids (including eight tea catechins, glycosides and aglycones), four coumarins plus caffeine were analysed within 20 min using ultra high performance liquid chromatography (UHPLC) with PDA detection. UHPLC system was equipped with C18 analytical column (100 mm × 2.1 mm, 1.7 μm), utilising 0.1% formic acid and methanol mobile phase in the gradient elution mode. The developed method was tested for the system suitability: resolution, asymmetry factor, peak capacity, retention time repeatability and peak area repeatability. The method was fully validated in the terms of linearity (r² > 0.9990 for all 30 compounds), range (typically 1-100 mg L⁻¹), LOD, LOQ, inter/intra-day precision (<3% and <9% respectively) and inter/intra-day accuracy (typically 100 ± 10%). Subsequently the method was applied to the identification (spectral information and peak purity calculations were profited) and quantification of phenolic compounds and caffeine present in tea infusions and extracts.     

Contribution to vapor generation-inductively coupled plasma spectrometric techniques for determination of sulfide in water samples

Vapor generation-inductively coupled plasma-optical emission spectrometry was used for the determination of sulfide in water samples preserved by the addition of a zinc acetate and sodium hydroxide solution. Hydrogen sulfide and acid-volatile sulfides were transformed, by acidification, to a gaseous phase in a vapor generator and subsequently detected by inductively coupled plasma optical emission spectrometry. Compounds interfering with iodometric titration and spectrophotometric determination were examined as potential chemical interferents. The proposed method provides results comparable to iodometric titration in the tested concentration range 0.06-22.0 mg L⁻¹. Limit of detection for the determination of hydrogen sulfide by this method is 0.03 mg L⁻¹.     

Synthesis of new sulfonic acid-containing oligosaccharide mimetics of sialyl Lewis A

Two trisaccharides as new sulfonic acid mimetics of the sialyl Lewis A tetrasaccharide were synthesized. The natural sialic acid residue is replaced by a C-sulfonic acid moiety attached to position C-3′ of the lactosamine unit of the mimetics. The l-fucose unit was also replaced by a d-arabinose ring in one of the analogues. Formation of the sulfonic acid moiety on the trisaccharide level could be successfully achieved by means of introduction of an acetylthio moiety into the galactose skeleton and subsequent oxidation. The equatorial arrangement of the acetylthio group linked to C-3 of the galactose ring could be achieved by double nucleophilic substitution; efficient formation of the gulo-triflate derivatives required low-power microwave activation. Oxidation of the acetylthio group was carried out using Oxone in acetic acid.