Materials Literature
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Elongational flow-induced crystallization behavior was investigated on supercooled liquids of two poly(ethylene naphthalate)s (PENs) with different crystallization habits via elongational flow optorheometry (EFOR), temperature-modulated differential scanning calorimetry (TMDSC), and Rayleigh scattering in the temperat…
ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTAromatic Benzannulated Silole Dianions. The Dilithio and Disodio Salts of a Silaindenyl Dianion1Seok-Bong Choi, Philip Boudjouk, and Pingrong WeiView Author Information Center for Main Group Chemistry, Department of Chemistry North Dakota State University, Fargo, North…
A microscopic model, which describes specific features of the electronic spectrum of various allotropic forms of amorphous carbon as being responsible for their structure peculiarities, is presented. It is shown that the formation of a double-well potential is a possible driving force for this behavior.
A series of highly congested polyphenylbiphenyls and polyarylfluorenes has been prepared and their X-ray structures determined. Decaphenylbiphenyl adopts a very unusual C 1 -symmetric geometry (rather than the more intuitive D 2 geometry) in which one of the central benzene rings is distorted into a boat conformation.…
Polymerization of lactones such as δ-valerolactone (VL) and ε-caprolactone (CL) with protic compounds proceeded in the presence of an aluminosilicate mesoporous zeolite Al−MCM-41 (pore diameter of 27 Å, surface area = 1010 m 2 g -1, and Si/Al = 17), to give polyesters with a narrow molecular weight distribution. A seq…
High molecular weight specimens of syndiotacticity-rich poly(vinyl alcohol) (PVA) have been prepared by saponification of copolymers of vinyl pivalate (VPi) and vinyl acetate (VAc). VPi and VAc were copolymerized using the low-temperature initiator 2,2‘-azobis(2,4-dimethylvaleronitrile) and saponified in KOH/methanol/…
Ultrathin multilayer films of a novel molybdenum(VI) polyoxometalate cluster ((NH 4 ) 21 [H 3 Mo 57 V 6 (NO) 6 O 183 (H 2 O) 18 ]) (Mo 57 ) and poly(allylamine hydrochloride) (PAH) have been prepared by the consecutive stepwise adsorption of Mo 57 and PAH from dilute aqueous solution. The Mo 57 /PAH multilayer films h…
Ferromagnetic systems described by the double exchange model are investigated. At temperatures close to the Curie temperature, and for a wide range of doping levels, the system is unstable toward phase separation. The chemical potential decreases upon increasing doping, due to the significant dependence of the bandwid…
We investigate the energy landscape of two dimensional network models for covalent glasses by means of the lid algorithm. For three different particle densities and for a range of network sizes, we exhaustively analyse many configuration space regions enclosing deep-lying energy minima. We extract the local densities…
Amphiphilic block copolymers containing a poly(styrene) tail and a charged helical poly(isocyanide) headgroup derived from isocyano-L-alanine-L-alanine and isocyano-L-alanine-L-histidine were prepared. Analogous to low-molecular mass surfactants, these block copolymers self-assembled in aqueous systems to form micelle…
The tunability and dielectric losses of ferroelectric (Ba,Sr)TiO3 film varactors were measured under DC voltage at microwave frequencies (~20 GHz). A new microwave two-pole tunable waveguide filter containing four ferroelectric (Ba,Sr)TiO3 film varactors was designed and tested. The frequency tuning of the filter resu…
The arrangement of the crystalline cellulose microfibrils in native flax fibers was studied by means of position-resolved microbeam X-ray small-angle scattering (μSAXS) at the ESRF. The nearly perfect alignment of the microfibrils parallel to the fiber axis could for the first time be determined directly on a single f…
New experimental evidence on the formation of spatio-temporal concentration patterns as imaged by photoemission electron microscopy (PEEM) supports our earlier kinetic model for subsurface oxygen formation in the CO oxidation reaction on Pt(110). Extensive experimental data on oxygen island growth and conversion is us…
A reinvestigation is reported of a prototype literature arene hydrogenation system, one previously believed to involve a [(C 8 H 17 ) 3 NCH 3 ] + [RhCl 4 ] - ion-pair catalyst. The methodology employed to uncover the true catalyst, and to deal with the classic and difficult mechanistic problem of “is it homogeneous or…
Various mechanisms to explain negative thermal expansion in oxides are presented. Our search for compounds having this unusual property has focused on the mechanism based on transverse thermal motion of oxygen in M−O−M linkages. Such a mechanism can give strong negative thermal expansion over broad temperature ranges.…
A series of zirconia powder samples with different crystallographic phases and surface areas, either prepared at the laboratory or obtained commercially, have been studied in relation to the interaction of CO 2 with their surfaces. Three complementary techniques such as infrared spectroscopy, adsorption microcalorimet…
Six polylactides, polymerized with Salen−Al−OCH 3 initiator and having optical purities between 43% and 100%, were analyzed by differential scanning calorimetry, X-ray diffraction, and optical microscopy, following various crystallization conditions. It was found that each of those polylactides can crystallize, even t…
An ab initio study on three hypothetical nitrogen−oxygen clusters is presented. The investigated systems are N 2 O 3, N 4 O 6, and N 8 O 12 with highly symmetric geometries, D 3 h, T d, and O h symmetry, respectively. Calculations were performed at SCF and MP2 level (MP2, for the two smallest clusters only). Several b…
ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTLinear Ferrocenylene−Siloxyl−Diacetylene Polymers and Their Conversion to Ceramics with High Thermal and Oxidative StabilitiesEric J. Houser and Teddy M. KellerView Author Information Materials Chemistry Branch, CODE 6127, Chemistry…
Traditionally it was thought that the unidirectional strength in the fiber direction of fiber dominated composites was not influenced by the matrix material. As long as the fiber was not affected then the strength would remain. However this thesis will challange that belief. The unidirectional strength in the fiber di…