Materials Literature
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A family of highly ordered mesoporous (20−300 Å) silica structures have been synthesized by the use of commercially available nonionic alkyl poly(ethylene oxide) (PEO) oligomeric surfactants and poly(alkylene oxide) block copolymers in acid media. Periodic arrangements of mescoscopically ordered pores with cubic Im 3̄…
We present a method for the direct measurement of the glass transition temperature of compressed gas–polymer systems. The technique utilizes a Setaram C80D microcalorimeter equipped with high-pressure cells. Pressurizing the cells and running in scanning mode allows direct determination of the glass transition tempera…
A novel series of water-soluble polyurethane surfactants has been prepared by the addition polymerization of 2,4 and 2,6-toluene diisocyanate 80 : 20%, respectively (TDI) to polyethylene glycol (PEG) and/or castor oil and ethylene glycol (EG). These water-soluble polyurethane surfactants have been found to exhibit exc…
Banana (Musa paradisica), Hemp (Hibiscus cannabinus), and Agave (Agave jourcroydes) fibers were treated with Novolac resin for the formation of their composites in the ratio of 50 : 50 (wt/wt). These fibers were also treated with maleic anhydride, and it was found that composites based on treated fibers showed higher…
Propylene–butene-1 copolymer (PBC) prepared with a titanium catalyst system was fractionated by temperature rising elution fractionation (TREF) over a temperature range of 5–80°C. PBC was shown to have a wide composition distribution ranging between 12–47 mol % of butene-1. Most of the fractions showed nearly the same…
Blends of maleated polypropylene and maleated ethylene propylenediene (EPDM-g-MA) were compounded in a twin-screw extruder with a polyetheramine (PEA), polyoxypropylenediamine, as a compatibilizer. The effect of the compatibilizer concentration and molecular weight on the physical properties was investigated. FTIR dat…
We consider in the article the influence of the irradiation and the internal sinks of the point defects on the rate of the flattening of the surface structure in solids. The irradiation produces only the additional external sources of point defects(vacancies and interstitial atoms). The general system of equations is…
Se han estudiado la microestructura y las propiedades mecánicas a 77 y 290 K de una serie de aleaciones Fe-xMn-3,2Al-0,23C con 12 ≤ x ≤ 43 (% en masa) con objeto de determinar los mecanismos que controlan la deformación plástica. Se ha comprobado que, en las aleaciones con estructura austenítica (Mn ≥ 22), el alargami…
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…