Uniaxial deformation and orientation of ethylene–tetrafluoroethylene films

This study concerns the thermal and mechanical response of several commercial grades of ethylene – tetrafluoroethylene copolymer films. Differential scanning calorimetry was used to show that, although films have similar degrees of crystallinity and melting temperature, the melting endotherms and crystallisation exotherms differ between materials, suggesting small changes in composition between manufacturers. Films were deformed in tension at a range of temperatures and rates. Selected films were unloaded immediately after stretching, and measurement of the elastic recovery highlighted further differences between materials. Batches of films were pre-drawn uniaxially above the glass transition and immediately quenched. When these materials were subsequently re-drawn below the glass transition temperature, most of them exhibited much improved yield stress, modulus and tensile strength (improving by factors of 5, 5 and 4, respectively at a draw ratio of 3), but a reduced strain to failure. In most of the films, the pre-drawing, as well as the initial orientation of the films, is accounted for by a simple shift in the true strain axis. This is indicative of a material response dominated by entropic network stretch. It also suggests that, in the cases where strain superposition does not work, a different arrangement of crystalline lamellae may be present, limiting the extent to which improved properties can be achieved in some materials.     

Water‐soluble metalated and non‐metalated A2B‐ and A3‐corrole/amino acid conjugates: syntheses,characterization and properties

In this study, novel water‐soluble corrole amino acid conjugates were synthesized and characterized. The coupling reaction of A₂B‐ and A₃‐corroles with glycine ethyl ester and taurine under strong basic conditions proved to be successful and yielded di‐ and trifunctionalized corrole amino acid conjugates in good yields. The subsequent metalation of the corrole/amino acid conjugates broadens the scope for applications considerably. As examples, we herein show the catalytic activity of the Mn(III) A₃‐corrole towards O₂ evolution. First we employed tert‐butyl hydroperoxide (t‐BuOOH) as oxidant to obtain the Mn(V)oxo species and tetrabutyl ammonium hydroxide (TBAH) as hydroxide donor agent. Furthermore, the binding properties of the non‐metalated and the Mn(III) A₃‐corrole/amino sulfonic acid conjugates and transport of proteins were investigated and the conjugates exhibited binding to human serum albumin (HSA). Finally, a novel Ga(III) A₃‐corrole/amino sulfonic acid derivative was synthesized and we briefly describe the photophysical properties of this compound. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis,Crystal Structure,and Selected Properties of [Au(S2CNH2)2]SCN: A Precursor for Gold Macro-Needles Consisting of Gold Nanoparticles Glued by Graphitic Carbon Nitride

A new preparation route is developed for the synthesis of needle-like crystals of [Au(S₂CNH₂)₂]SCN, which avoids disproportionation of the Au^I salt used as a starting material. In the crystal structure, the two crystallographically independent Au^III centers are in a square-planar environment of two S₂CNH₂ ligands. The Hirshfeld surface analysis reveals the presence of noncovalent intermolecular S⋅⋅⋅S interactions, which are essential for the spatial arrangement of the molecules. Density functional theory (DFT) calculations including dispersion and damping corrections result in a unit cell volume very close to the value determined experimentally. Thermal decomposition in an inert atmosphere generates black needles with lengths of up to 500 μm. X-ray powder diffraction and pair distribution function analyses demonstrate that the needles are composed of nanosized crystals with a volume-weighted average domain size of 20(1) nm. According to results of X-ray photoemission experiments, the black needles are covered by a nitrogen-rich carbon nitride with composition near (CN)₂N. ¹³C solid-state NMR investigations indicate that two different carbon species are present, with signals corresponding well to heptazine units as in melon and triazine units as in poly(triazin imide) type compounds. Scanning transmission electron microscopy tomography evidences that the needles are composed of slightly elongated nanoparticles.     

Crystal Structure of LiRh-type IrZn Determined by Powder X-ray and Selected Area Electron Diffraction

The LiRh-type crystal structure of the equiatomic intermetallic compound IrZn turns out to be a competitor to the otherwise energetically favored CsCl-type structures of congeneric transition metal zinc phases, thus enlightening the structural impact of element-specific factors beyond the Hume-Rothery concept.     

Reaktion von Pyridin-2-Carbonsäure Mit Tetrabutylammonium-Tetrachloro-Nitridotechnetat(VI) Sowie Tetrabutylammonium-Tetrachlorooxotechnetat (V)

Abstract

The reaction of 2-pyridine carboxylic acid (Hpic) with (n-Bu₄N)[TcNCl₄] and (n-Bu₄N)[TcOCl₄] in ethanol and methanol, respectively, yields the dinuclear μ-oxo complex [(pic)₂NTc-O-TcN(pic)(Hpic)Cl] and the monomeric complex [TcO(pic)₂Cl].

Visible and infrared spectroscopy, ESR, ¹H-NMR and ⁹⁹Tc-NMR have been used to characterize the new compounds. The most important field of application for the new compounds synthesized is radiodiagnostics.     

Gels dried under supercritical and ambient conditions: a comparative study and their subsequent conversion to silica–carbon composite aerogels

In present work, we have prepared gels with various compositions of methyltrimethoxysilane—3-(2,3-epoxypropoxy) propyltrimethoxysilane (MTMS-GPTMS) using a two-step acid base sol–gel process. To make a comparative study between the two common drying routes, we prepared gels under supercritical and also under ambient conditions. The density of the supercritically dried hybrid aerogels lies between 0.18 and 0.31 gcm^?3, while the density of the ambient dried ones ranges between 0.35 and 0.42 gcm^?3. The surface area of MTMS-0.25 GPTMS aerogel dried under supercritical conditions, has been found to be 464 m² g^?1 with a pore volume and average pore diameter of 1.24 cm³ g^?1 and 11 nm respectively. The same composition dried under ambient conditions is found to have similar properties i.e. a BET surface area of 439 m² g^?1, pore volume of 1.22 cm³ g^?1 and average pore diameter of 11 nm. The aerogels were later pyrolyzed yielding silica/carbon composite aerogels. The pyrolized aerogels possessed a surface area as high as 207 m² g^?1 with a total pore volume of 0.98 cm³ g^?1. The pyrolysed aerogels were also calcined to yield carbon free materials.