Solvatochromism of catechol derivatives – solute/solvent interactions

The solvatochromism of nine push–pull substituted catechol derivatives has been studied in a set of 39 various solvents. The influence of successive methyl substitution at the catechol OH groups on the extent of the solvatochromic shift has been investigated. The positive solvatochromism of 2‐(3,4‐dihydroxybenzylidene)‐2H‐indene‐1,3‐dione amounts 4360 cm^–1, which ranges from toluene to hexamethyl‐phosphoric triamide. To the best of our knowledge, it is one of the largest positive solvatochromic extent measured for a positive solvatochromic dye, comparable with Brooker's thiobarbituric acid with an extent of 4400 cm^–1. The detailed analyses of the solvatochromism were carried out by alternatively using the Kamlet–Taft and Catalán solvent parameters to achieve information of dipolarity versus polarizability effects of solvent upon solvatochromic properties. In solvents with high β values such as alcohols (0.66 < β < 0.90), amides (0.48 < β < 0.80), dimethyl sulfoxide (β = 0.76), tetramethyl urea (β = 0.80) and hexamethyl‐phosphoric triamide (β = 1.05) UV–Vis absorption spectra show two separate λ_max, which are caused by a deprotonation reaction. The solvatochromic behaviour of the anionic species is compared with those of the catechol derivatives. Copyright © 2012 John Wiley & Sons, Ltd.     

Non-isothermal flow of polymer melts in a curved tube

The results of a numerical study (using finite differences) of heat transfer in polymer melt flow is presented. The rheological behaviour of the melt is described by a temperature-dependent power-law model. The curved tube wall is assumed to be at constant temperature. Convective and viscous dissipation terms are included in the energy equation. Velocity, temperature and viscosity profiles, Nusselt numbers, bulk temperatures, etc. are presented for a variety of flow conditions. Br — Brinkman number - c specific heat, J/kg K - De — Dean number - E dimensionless apparent viscosity, eq. (14d) - G dimensionless shear rate, eq. (19) - k parameter of the power-law model, °C^–1, eq. (7) - mass flow rate, kg/s - m ₀ parameter of the power-law model, Pa · s ⁿ , eq. (7) - n parameter of the power-law model, eq. (7) - Nu 2r _p/ — Nusselt number, eqs. (28,31) - p pressure, Pa - Pe — Péclet number - P —(p/)/r _c — pressure gradient, Pa/m - dissipated energy, W, eq. (29) - total energy, W, eq. (30) - r radial coordinate, m - r _c radius of tube-curvature, m, fig. 1 - r _p radius of tube, m, fig. 1 - r _t variable, m, eq. (6) - R dimensionless radial coordinate, eq. (14a) - R _c dimensionlessr _c, eq. (14a) - R _t dimensionlessr _t, eq. (14a) - t temperature, °C - bulk temperature, °C, eq. (27) - t ₀ inlet temperature of the melt, °C - t _w tube wall temperature, °C - T dimensionless temperature, eq. (14c) - T _w dimensionless tube wall temperature - T dimensionless bulk temperature - u ₁ variable, s^–1, eq. (4) - u ₂ variable, s^–1, eq. (5) - U ₁ dimensionlessu ₁, eq. (18) - U ₂ dimensionlessu ₂, eq. (18) - v velocity in-direction, m/s - average velocity of the melt, m/s - V dimensionlessv, eq. (14b) - dimensionless , eq. (15) - z r _c — centre length of the tube, m - Z dimensionlessz, eq. (14e) - heat transfer coefficient, W/m² K - shear rate, s^–1, eq. (8) - — shear rate, s^–1 - apparent viscosity, Pa · s, eq. (7) - ₀ — apparent viscosity, Pa · s - angular coordinate, rad, fig. 1 - thermal conductivity, W/m K - melt density, kg/m³ - axial coordinate, rad, fig. 1 - rate of strain tensor, s^–1, eq. (8) - (—p) pressure drop, Pa     

Extended balance of linear momentum from higher gradient stress field theory

We present the equation of linear momentum considering higher gradients for stress and body force. Both are approximated via Taylor series expansion within a finite Cauchy cube of dimensions L_c. Whereas linear terms of the series expansion result to the classical balance of linear momentum, terms up to third order yield an extended balance equation. The extension includes an internal length scale L²_c caused by surface integrals on the cube. The approach makes use of Cauchy's theorem and standard Newtonian mechanics but constitutive assumptions are not applied. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dynamical localization and eigenstate localization in trap models

The one-dimensional random trap model with a power-law distribution of mean sojourn times exhibits a phenomenon of dynamical localization in the case where diffusion is anomalous: the probability to find two independent walkers at the same site, as given by the participation ratio, stays constant and high in a broad domain of intermediate times. This phenomenon is absent in dimensions two and higher. In finite lattices of all dimensions the participation ratio finally equilibrates to a different final value. We numerically investigate two-particle properties in a random trap model in one and in three dimensions, using a method based on spectral decomposition of the transition rate matrix. The method delivers a very effective computational scheme producing numerically exact results for the averages over thermal histories and initial conditions in a given landscape realization. Only a single averaging procedure over disorder realizations is necessary. The behavior of the participation ratio is compared to other measures of localization, as for example to the states’ gyration radius, according to which the dynamically localized states are extended. This means that although the particles are found at the same site with a high probability, the typical distance between them grows. Moreover the final equilibrium state is extended both with respect to its gyration radius and to its Lyapunov exponent. In addition, we show that the phenomenon of dynamical localization is only marginally connected with the spectrum of the transition rate matrix, and is dominated by the properties of its eigenfunctions which differ significantly in dimensions one and three.     

Mechanochemical Synthesis and Characterization of Hydrated and Dehydrated Crystalline Strontium Terephtalates

A successful mechanochemical synthesis of strontium terephthalate trihydrate is described for the first time. The dehydration of Sr(C₈H₄O₄) · 3H₂O occurs at about 100 °C and results in a well‐defined strontium terephtalate, Sr(C₈H₄O₄), thermally stable up to 550 °C. Both compounds are not described so far in the literature. Their structures were solved by ab initio structure determination and subsequent Rietveld refinement of the powder diffraction data. Further methods like DTA‐TG, MAS NMR and FT‐IR spectroscopy, and BET measurements were used to characterize these compounds.     

Setup for evaluation of fatigue crack growth in rubber: Pure shear sample geometries tested in tension-compression mode

A novel measurement setup is developed to determine fatigue crack growth and heat build-up in rubber. Loading conditions include tensile and compressional loads. Deviations in the crack shape are detected with special features (swivel arm and additional light sources) and provide the possibility of a subsequent manual correction of the shadow crack length. This results in improved reproducibility and a worst-case scenario is obtained.