Materials Literature
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We report a neutron and x-ray Rietveld analysis of strontium titanate down to 1.5 K. The results do not show evidence for any supplementary structural phase transition or local frozen polar ordering. These results are a supplementary indication that at very low temperature strontium titanate should display only weak l…
Spherical MnAs ferromagnetic particles with controllable diameters (5–30 nm) are embedded in a high quality GaAs matrix. The particles are formed in a two step process consisting of the epitaxy of a homogeneous Ga1−xMnxAs layer at low temperatures using molecular beam epitaxy followed by phase separation upon annealin…
In 1953, Ter-Mikaelian predicted that low energy bremsstrahlung from relativistic electrons moving through a medium is suppressed, because of interactions between the emitted photon and the electrons in the medium. This suppression occurs because the emission takes place on a long distance scale, allowing for destruct…
The accelerated photoaging of solid and liquid silicones is reviewed, and particular attention is paid to the influence of the main substituents of silicone chemistry. The decomposition of functional groups as -H, -CH=CH 2, -CH 2 -CH 2 -, -CH 2 -CH 2 -CH 2 OH, and -Ph was followed mainly by Fourier transform IR, 1 H-,…
With a view to developing new materials for technological applications, the theory and mechanism of nonlinear optical phenomena in various dielectric media are reviewed. The role of theoretical modeling in advancing our understanding of the structure-property relationships of nonlinear optical materials is discussed.
A range of analytical techniques was used to characterize the conversion products of a common polyolefin processing stabilizer (Irgafos 168, a hindered phosphite) and a common polyolefin antioxidant (Irganox 1076, a hindered phenol). Analysis by gas chromatography (GC)-mass spectrometry revealed that the phosphite sta…
We used temperature and time-dependent changes in vinyl and vinylidene concentration to develop a kinetic model that allows estimation of whether cross-linking or thermal scission will dominate during melt processing of major classes of polyethylenes (PE). Torque rheometer processed high-density, linear low-density-,…
Poly(aryl ethers) are an important class of commercial polymers and are a member of the family of materials referred to as engineering thermoplastics ( 1 ). Commercial examples include Amoco's poly(aryl ether sulfone) (Udel), ICI's poly(ether ether ketone) (PEEK), and General Electric's Ultem poly(ether imide). They d…
It is generally recognized that in order to improve the environmental acceptability of household laundry detergents, biodegradble replacements for the polycarboxylate components of these detergent formulations are needed. Although the poly(acrylic acid) homopolymers and copolymers currently in use are not considered h…
The changes in mechanical properties of several polymers induced by high energy protons (10, 30 and 45 MeV protons) were studied and compared with those induced by 2 MeV electrons and Co-60 gamma rays. Changes in elongation at break showed the same trends for 10 MeV proton and electron irradiations in the case of both…
Density-functional theory (DFT) is a promising method for the calculation of molecular optical properties, since it is less computationally demanding than other ab initio methods, yet typically yields results of a quality comparable to or better than those from the Hartree-Fock approximation. The calculation of static…
This survey concerns the major features of stability, thermal degradation, and stabilization of poly(vinyl chloride) (PVC). The effect of microstructure and chain defects of PVC on the stability of the resin is analyzed and reviewed in the light of recent findings. New experimental results of thermal degradation of PV…
We describe a study aimed at validating the Arrhenius lifetime prediction methodology. Ultimate tensile measurements were made on three elastomers after elevated temperature exposures. Although tensile elongation could be analyzed using the Arrhenius approach, tensile strength could not. Modulus profiles resolved this…
With a view to developing new materials for technological applications, the theory and mechanism of nonlinear optical phenomena in various dielectric media are reviewed. The role of theoretical modeling in advancing our understanding of the structure-property relationships of nonlinear optical materials is discussed.
Sterically hindered phenols are efficient stabilizers against the degradation of polymers upon processing of the melt. They also protect the polymer during end-use and impart protection against the loss of chemical, physical, and aesthetic properties. Combinations of sterically hindered phenols with hydroperoxide deco…
The changes in mechanical properties of several polymers induced by high energy protons (10, 30 and 45 MeV protons) were studied and compared with those induced by 2 MeV electrons and Co-60 gamma rays. Changes in elongation at break showed the same trends for 10 MeV proton and electron irradiations in the case of both…
Chain transfer to monomer during the free-radical polymerization of vinyl chloride is shown to occur, in part, by a mechanism that begins with the abstraction of methylene hydrogen from the polymer by a propagating macroradical The resultant radical then donates a chlorine atom to the monomer to form an allylic struct…
A copper(I)-templated synthesis furnishes rotaxanes, in which porphyrin subunits serve as bridges and bulky stoppers and the threaded rings contain chelating phenanthroline groups. A [5]rotaxane is shown schematically on the right, ○ = CuI, thick lines = phenanthroline units, ⋄ = porphyrins.
Either a metal atom or the phthalocyanine ligand is the site of the first oxidation of the heteronuclear triple-decker complexes of type 1, depending on whether they contain an oxidizable CeIII ion or not. Now the first X-ray structure of such a heteronuclear triple-decker complex (1, M Ce, M′ Gd, p oep) has als…
Eine richtige Doppelbindung zwischen den beiden Imidazol‐2‐yliden‐Hälften kennzeichnet das bei Raumtemperatur stabile Tetraazafulvalen 1 , dessen Dissoziation zu 1 ′ nicht nachzuweisen ist, obwohl die Bindungsstärke auf nur wenige kcal mol −1 geschätzt wird. Diese stimmt gut mit theoretischen Vorhersagen überein, die…