Materials Literature
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We report defect-resonance patterns associated with two kinds of low-concentration defects typically found in metallocene-synthesized isotactic polypropylenes (iPP's). These defects are the simple mrrm stereo defect and the regio 2,1-erythro defect. This work is a critical part of our effort to determine the extent to…
A cobalt porphyrin equipped with two different but geometrically complementary pyridine ligands self-assembles to form an unusually stable complex with approximately 12 porphyrin monomers arranged in a macrocyclic array.
The aerobic reaction of Cr(CO)6 with tris(pentafluorophenyl)corrole (H3(TpFPC)) in toluene gives the dark red oxochromium(V) compound (TpFPC)Cr(O), which has been characterized by X-ray crystallography, electrochemistry, and EPR spectroscopy. Short Cr-N (1.927-1.943 A) bonds as well as relatively large 14N and small 5…
We have performed a molecular dynamics simulation study of atactic polystyrene (a-PS) and its dimer 2,4-diphenylpentane (DPP) using a previously derived quantum chemistry based explicit atom force field. The X-ray structure factor of a-PS obtained from simulations was found to be in good agreement with experiment, rep…
A family of diphenylethyne-linked porphyrin dimers and trimers has been prepared via a building block approach for studies of energy-transfer processes. The dimers contain Mg and Zn porphyrins (MgZnU); the trimers contain an additional free base porphyrin (MgZnFbU). In both the dimers and trimers, sites of attachment…
A bulk polycrystalline sample of YBa_{2}Cu_{3}O_{7-δ} (δ\approx 0.1) has been irradiated by γ-rays with ^{60}Co source. Non-monotonic behavior of T_c (defined as the temperature at which normal resistance is halved) with increasing irradiation dose Φ(up to about 220 MR) is observed: T_c decreases at low doses (Φ\leq 5…
We present analytic approximations for the field, temperature, and orientation dependences of the interface velocity in a two-dimensional kinetic Ising model in a nonzero field. The model, which has nonconserved order parameter, is useful for ferromagnets, ferroelectrics, and other systems undergoing order-disorder ph…
The self-aggregation of cationic porphyrins in aqueous solution has been studied by means of absorption, 1 H NMR, and resonance light scattering spectroscopy. The aim of the present study is clarification of the factors which most influence porphyrin self-aggregation in water. Cationic 5,10,15,20-tetrasubstituted porp…
Standard electrochemical data for high-quality, boron-doped diamond thin-film electrodes are presented. Films from two different sources were compared (NRL and USU) and both were highly conductive, hydrogen-terminated, and polycrystalline. The films are acid washed and hydrogen plasma treated prior to use to remove no…
Two years after the first light of UT1 a summary of the On- site optical maintenance situation seems necessary. A comparison with the Maintenance Program developed in Europe will be commented. Measured data on the large mirrors and the efforts to maintain and improve the on-site contamination at a low level will be pr…
The structural, kinetic and photophysical properties of bimetallic lanthanide complexes with simple calix[n]arenes (n = 5 and 8) are discussed. The intensity of the f-f transitions of the Eu(III)-containing edifices strongly depends on the mixing between 4f and ligand-to-metal charge-transfer (LMCT) wave functions. In…
Poly(ethylene glycol) (PEG) has long been recognized for its unusual ability to resist protein adsorption. This is attributed to the repulsion of proteins by the polymer segments. Despite its successes, there are several reports that PEG does weakly bind proteins. This work tests the hypothesis that the PEG can bind t…
Transport behavior of trivalent solutes across mesoporous Anopore γ-alumina membranes was investigated as a function of pore diameter, pH, ionic strength, and nature of the salt in solution. Radiotracers, 55 Fe, 152 Eu, 157 Tb, and 241 Am, were present in the feed solutions at concentrations ranging from 10 - 8 to 10…
Sensitized photocurrent generation is observed with a porphyrin dyad (P Zn -P) and its structural moieties: 5-(4-carboxyphenyl)-10,15,20-tris(4-methylphenyl) porphyrin (P) and Zn(II) 5-(4-carboxyphenyl)-10,15,20-tris(4-methylphenyl) porphyrin (P Zn ) . The dyes were adsorbed to saturation on a nanocrystalline SnO 2 th…
The adsorption properties of the precipitated Fe and FeMn catalysts were studied by in-situ diffuse reflectance FTIR using CO, NO and CO + H 2 (syngas) as probe molecules. CO and NO adsorption on the oxidized Fe sample reveals the presence of Fe(III) and Fe(II) on the surfaces. On the H 2 -reduced Fe sample, the adsor…
ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTPolyphosphazene−Polystyrene Copolymers: Block and Graft Copolymers from Polyphosphazene and Polystyrene MacromonomersRobbyn Prange, Scott D. Reeves, and Harry R. AllcockView Author Information Department of Chemistry, The Pennsylvan…
The effect (Stark effect) of an applied electric field on the electronic states of molecular adsorbates was studied by measuring surface plasmon resonance (SPR) as a function of the wavelength of the incident light that excites the SPR. Using the Kramers-Kronig relation, Stark spectra comparable to those obtained with…
The charge carrier dynamics in illuminated nanoporous ZnO electrodes consisting of 5 nm particles were investigated. Stable photocurrent quantum efficiencies of 15−30% and photovoltages of up to 0.4 V were found in the presence of the I - /I 3 - redox couple in propylene carbonate. The electronic transport in these Zn…
A unique interfacial reactivity of self-assembled mesostructured silica−surfactant systems toward organosilanes was utilized to obtain ordered mesoporous materials such as MCM-41 with different surface functionality. The idea of this process is based on a direct replacement of electrostatic interactions between negati…
Poly(butylene terephthalate) (PBT) was depolymerized in excess methanol at high-temperature (473–523 K) and high-pressure (4–14 MPa) conditions. Considering the critical point of methanol (512.6 K, 8.09 MPa), the reaction pressure was varied over the range of 6–14 MPa at the reaction temperature of 513 K. As a result,…