Materials Literature
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Abstract Changes in the thermal transition and stiffness of ionomers occuring during aging or water absorption were investigated. Ionomers used in this study are Na, K, Mg, and Zn salts of poly(ethylene‐ co ‐methacrylic acid) (EMAA), whose methacrylic acid unit is 5.4 mol %. It was found that ionomer stiffness is subj…
In the course of glutamate fermentation by Acidaminococcus fermentans glutaconate coenzyme A-transferase catalyzes the transfer of CoAS- from acetyl-CoA to (R)-2-hydroxyglutarate, forming (R)-2-hydroxyglutaryl-CoA. Glutamate (E) 54 of the beta-subunit was postulated to be directly involved in catalysis by formation of…
The chromophyte algae are a large and biologically diverse assemblage of brown seaweeds, diatoms, and other golden algae classified in 13 taxonomic classes. One subgroup (diatoms, pedinellids, pelagophytes, silicoflagellates, and certain enigmatic genera) is characterized by a highly reduced flagellar apparatus. The f…
Abstract Reactions taking place in a system consisting of a diepoxide (DGEBA, diglycidylether of bisphenol A) and a diisocyanate (TDI 80 : 20, toluene diisocyanate), catalyzed by a tertiary amine (BDMA, benzyldimethylamine), were followed by differential scanning calorimetry (DSC), infrared spectroscopy (FTIR), and ch…
Abstract The hydrolytic aging of an unstabilized industrial sample of polycarbonate was studied at 40, 70, 80, and 90°C, 100% RH. The water absorption characteristics show that, at equilibrium, the polymer absorbs about 0.04 mol water per ester group and that the equilibrium is reached after about 10–40 h exposure, i.…
Abstract The contribution of elastomer polarity and reactivity to bound rubber formation has been investigated. In this study, a number of elastomers of different chemical nature have been tested. The surface of the carbon black (N110) has also been modified by nitric acid oxidation in order to increase the concentrat…
A water-soluble β-cyclodextrin bearing seven naphthoate chromophores forms a very stable 1:1 inclusion complex (shown right) with a merocyanine dye, which mimics the antenna effect in photosynthetic units. The energy transfer from the naphthoate chromophores to the merocyanine is shown to take place with 100 % efficie…
Almost rectangular cavities can be seen in the structure of the title compound (part of the crystal structure shown on the right), the first heteropolyoxo-tungstate with defined micropores. The compound was prepared in a hydrothermal reaction with W, WO3, H3PO4, H2O, and hexamethylenediamine. Potential applications of…
Not just the size but also the multiplication of functions possible through branching is at the forefront of dendrimer chemistry. Owing to the numerous recent key publications by Newkome, Fréchet, Moore, Majoral, Meijer, and others, this Highlight has the dimensions of a minireview.
Abstract Plaques of bisphenol A polycarbonate (PC) were exposed to a water‐saturated atmosphere at temperatures ranging from 40 to 90°C for up to 7 months. Certain samples were exposed under tensile load at 60 and 90°C, 100% RH with stresses ranging from 3.7 to 8.7 MPa. The PC molecular weight was determined by steric…
Mn(ClO4)2 ·6H2O, 2,2'-bipyridine, and NaN3 were used to synthesize [Mn(N3)2-(bpy)]χ, the crystal structure of which (shown below) is characterized by alternating end-on and end-to-end bridging azido ligands. The existence of alternating ferro-and antiferromagnetic interactions between the S = 5/2 ions, as found previo…
The saddle‐shaped porphyrin with the largest deviation from planarity observed to date is found in the crystal structure of [H 4 obrtpp][CF 3 COO] 2 · 0.5 CHCl 3 (H 2 obrtpp = octabromotetraphenylporphyrin). The pyrrole rings in the porphyrin are twisted by 62° with respect to each other, and the β‐pyrrole C atoms are…
Abstract Nanocomposites were produced via sol–gel reactions for tetraethylorthosilicate within the cluster morphology of perfluorosulfonic acid films. Small‐angle x‐ray scattering revealed that the polar/nonpolar nanophase‐separated morphological template persists despite invasion by the silicon oxide phase. Scanning…
Abstract We synthesized nylon 6‐clay hybrid materials using four types of clay minerals, montmorillonite, saponite, hectrite, and synthetic mica. The mechanical properties of their injection molded specimens were measured according to ASTM. Nylon 6‐clay hybrid using montmorillonite was superior to the other hybrids in…
A theoretical and experimental study of the electronic and magnetic structure of Fe 2 P 1-x Si x is performed. A hexagonal-orthorhombic crystal structure transition occurs with increasing Si substitution. The latter crystal structure is extremely complex with six inequivalent Fe sites. The magnetic moments, as obtaine…
We have studied the formation of cuspidal pits during the growth of strained SixGe1−x alloy layers at relatively high supersaturations. The pit formation is directly linked to strain in the alloy layer, and we propose a heterogeneous formation mechanism in which the pits develop from stress-driven surface diffusion as…
Photoluminescence spectra from the Si impurity center in diamond films grown by chemical-vapor deposition techniques were studied at temperatures between 9 and 300 K. Laser excitation at 514.5 nm, and resonant with the zero-phonon absorption line at 737 nm (1.6823 eV), were used. Luminescence lines become narrowed at…
Leakage currents in epitaxial ferroelectric/perovskite-conductor heterostructures reproducibly show diode properties having hysteresis. The hysteresis appears in forward bias, which is positive for electron (n) type conductors and negative for hole (p) type conductors. The hysteresis is due to the increase of conducti…
The energy distribution of ${L}_{3}{M}_{4,5}{M}_{4,5}$ Auger electrons emitted from solid Ag is studied as a function of the exciting photon energy in the ${L}_{3}$ threshold region. The $^{1}G_{4}$ Auger line not only exhibits a Raman-type energy dispersion and a reduced core hole lifetime broadening, but its line sh…
A new, step bunching instability in the growth of stepped surfaces by molecular beam epitaxy MBE is described. It is produced by an elastic mechanism, and is different from the instability discovered by Asaro and Tiller and by Grinfeld. Unlike the Asaro-Tiller-Grinfeld instability (which is expected to occur only unde…