Materials Literature
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The electronic structure of amorphous silicon nanoclusters is calculated within the empirical tight-binding approximation. The electronic states are classified into three groups: extended and weakly and strongly localized. The last category practically disappears in hydrogenated amorphous silicon clusters for which th…
The oxidation of single crystal gallium nitride in dry air has been investigated. X-ray photoelectron spectroscopy (XPS) revealed minimal oxide growth at 450 and 750 °C for up to 25 h. However, at 900 °C the growth of an oxide approximately 5000 Å thick was observed after 25 h. This oxide was determined to be the mono…
There are two current ways to evaluate the adiabatic corrections to a potential energy hypersurface: firstly a rigorous way in which one starts with the separation of the centre-of-mass motion and where one gets rather complicated expressions in terms of relative coordinates in a molecule-fixed frame, and secondly a p…
This is the second part of a study of chemical structure-physical property-performance relationships among several fluoropolymers and liquid penetrants, focusing on their permeation behavior. That behavior was consistent with the chemical and physical characteristics of the polymers, in that it depended on thermodynam…
In exzellenter Ausbeute ist das Carbaporphyrin 1 durch Anwendung der „3 + 1”︁‐Strategie zugänglich. Dabei wird Inden‐1,3‐dicarbaldehyd in Gegenwart von 5proz. Trifluoressigsäure in Dichlormethan mit einem Tripyrran umgesetzt. Das verwandte Formylcarbaporphyrin 2 wurde auf ähnlichem Wege hergestellt. Entgegen früheren…
This is the first part of a study of chemical structure-physical property-performance relationships among several fluoropolymers and liquid penetrants, focusing on their diffusivities and solubilities. Transient sorption experiments conducted with perfluoroalkoxy, fluorinated ethylene propylene, and ethylene tetrafluo…
The activation energy and rate constants for the decomposition of sodium persulfate in the presence of acrylic acid have been determined for monomer compositions representative of those used in a polymerization process to prepare sodium polyacrylate superabsorbent polymers. It was found that, relative to buffered aque…
Volume-averaging techniques developed for modeling drying processes in porous materials offer a convenient framework for analyzing vapor sorption in porous hygroscopic polymeric materials. Because of the large temperature changes associated with water vapor sorption in these materials (from 10° to 20°C), sorption/diff…
Regioregular poly(ferrocenylsilane)s 1, end-group-functionalized polymers of controlled molecular weight, and novel graft copolymers 2 are accessible by transition-metal-catalyzed ring-opening polymerization of strained ferrocenophanes at ambient temperature.
The creation of new materials may be possible by searching out high-energy forms of solid-state structures. In his Perspective, Brus discusses results reported in the same issue by Chenet al. on direct measurements of structural changes in nanocrystals. The measurements show that metastable higher-energy forms are mor…
Twenty four hydrogen bonds of the type ROH…︁−OSi bind the double six-ring silicate components and the oligosaccharide α-cyclodextrin (α-CD) in K12Si12O30 · 2α-CD·36H2O (1, tetrahedral representation depicted on the right). Thus, α-cyclodextrin is is incorporated in an unusual way as a multidentate hydrogen-bond don…
Poly(vinyl acetate) (PVAc)/poly(ethylene oxide) (PEO) blends were prepared by casting from either benzene or chloroform. The solvent effects on the crystallization behavior and thermodynamic properties of the blends were studied by the differential scanning calorimeter (DSC). Two grades of PEO with different molecular…
Polypyrrole films doped with p-toluenesulfonate and poly(4-styrenesulfonate) anions were synthesized electrochemically. These films were treated with water and dilute NaOH solution for varying periods of time. The films do not lose the anions readily when treated with water. In NaOH, dedoping occurs rapidly, either vi…
The lack of suitable crystals has meant that it has not been possible to carry out a conventional single-crystal X-ray structure analysis to determine the structure of red fluorescein. Instead, the application of a Monte Carlo method has allowed the crystal structure to be determined directly from powder X-ray diffrac…
Macrocyclization of 2,3-dicyano-1,4-diox-2-ene with magnesium propoxide in propanol provided the enantiomerically pure C4-symmetric (porphyrazinato)magnesium(II) complex 1. The structure of the macrocycle was confirmed by an X-ray crystallographic study on the demetalated porphyrazine.
The use of adhesives is widespread and growing, and there are few modern artefacts, from the simple cereal packet, to the jumbo jet, that are without this means of joining. Adhesion Science provides an illuminating account of the science underlying the use of adhesives, a branch of chemical technology which is fundame…
The three-dimensional structure of the enzyme 3-oxo-delta5-steroid isomerase (E.C. 5.3.3.1), a 28-kilodalton symmetrical dimer, was solved by multidimensional heteronuclear magnetic resonance spectroscopy. The two independently folded monomers pack together by means of extensive hydrophobic and electrostatic interacti…
The crystal structure of the arabinose-binding and dimerization domain of the Escherchia coli gene regulatory protein AraC was determined in the presence and absence of L-arabinose. The 1.5 angstrom structure of the arabinose-bound molecule shows that the protein adopts an unusual fold, binding sugar within a beta bar…
The problem of Fermi-level pinning at semiconductor-metal contacts is readdressed starting from first-principles calculations for Al/GaAs. We give quantitative evidence that the Schottky barrier height is very little affected by any structural distortions on the metal side---including elongations of the metal-semicond…
The kinetics of a first-order, solid-solid phase transition were investigated in the prototypical nanocrystal system CdSe as a function of crystallite size. In contrast to extended solids, nanocrystals convert from one structure to another by single nucleation events, and the transformations obey simple unimolecular k…