bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hygrothermal Aging Effects in Cured Epoxies
Authors: Barrie James A. , Rudd Howard , Sagoo Perminder S. , Johncock Peter 
Published: April 2007

AbstractThe effect of relatively severe hygrothermal aging on the sorption and also the diffusion of water at 40°C has been studied for a number of epoxy networks comprising tetraglycidyl 4,4′‐diaminodiphenyl methane, and the curing agent 4,4′‐diaminodiphenyl sulphone, 4,4′‐diaminodiphenyl methane and 2,2′‐dichloro‐4,4′‐diaminodiphenyl methane. Aging at high temperatures is accompanied by a pronounced increase in sorptive capacity at 40°C consistent with a significant expansion of the network. Dry annealing of the aged network at sub‐ Tg temperatures collapses the expanded structure to recover the sorptive capacity of the unaged network. Preliminary studies of the sorption‐desorption kinetics for aged networks indicate that the effective diffusion coefficient is not markedly affected.
A Comparison of the Phase Behaviour of Polystyrene in Cycloalkanes and n‐Alkanes
Authors: Cowie John M. G. , McEwen Iain J. 
Published: April 2007

AbstractCloud point curves for several narrow fractions of polystyrene dissolved in cycloheptane, in cyclooctane and in cyclodecane have been established, and the critical solution temperatures extrapolated to give the respective temperatures. All three cycloalkanes are good solvents for the polymer. A comparison is made between the phase behaviour of polystyrene dissolved in cyclic alkanes and in n‐alkanes using free volume polymer solution theory.
Selective Chlorination of Side‐chains in Friedel‐Crafts Polymers
Authors: Blincow Philip J. , Ghotra Joginder S. , Pritchard Geoffrey 
Published: April 2007

AbstractAralkyl polymers with ethyl side‐chains were prepared by Friedel‐Crafts reactions. Ethylbenzene and bis(p‐chloromethyl)benzene (BCMB) were reacted together in the presence of stannic chloride to produce polymers of various molecular weights. A study was then carried out of the chlorination of these polymers, using (a) molecular chlorine, (b) molecular chlorine with a peroxide catalyst and phosphorus pentachloride, (c) sulphuryl chloride. The objective was to determine the best conditions for chlorination to occur selectively at the α‐carbon atom of the ethyl group, with minimal chlorination at either the β‐position or the main‐chain methylene groups. Analysis of 1H nuclear magnetic resonance spectra of the chlorinated polymers suggests that in most cases chlorination occurs extensively both in the side‐chain and in the main‐chain methylene groups. Conditions were found, however, which favour chlorination at the α‐position. The greatest selectivity was achieved when molecular chlorine, a peroxide catalyst and phosphorus pentachloride were used in benzene solvent.
Interpretation of intrinsic viscosity/temperature data for solutions of poly(phenyl acrylate) and poly(ethylene oxide)
Authors: Gregory Peter , Huglin Malcolm B. , Khorasani Mohamad K. H. , Sasia Pedro M. 
Published: April 2007

AbstractMeasured intrinsic viscosities ([η]) at several temperatures (T) within the interval 280–350 K have been found to increase with T for solutions of poly(phenyl acrylate) (PPA) in ethyl lactate. A decrease of [η] with T was observed for aqueous solutions of poly(ethylene oxide) (PEO) at several temperatures within the range 276–358 K. The results have been treated on the basis of eight excluded volume theories, among which the best consistency was afforded by those of Kurata‐Stockmayer‐Roig, Fixman, and Stockmayer (Padé). These yielded values of −3.4 × 10−3 to −4.7 × 10−3 deg−1 and −0.9 × 10−3 to −2.4 × 10−3 deg−1 for the temperatur coefficient of the unperturbed dimensions of PPA and PEO, respectively. The derived θ‐temperatures were 287 K as the upper critical solution temperature for PPA in ethyl lactate and 365–382 K as the lower critical solution temperature for aqueous PEO.
Silicones as biomaterials
Authors: Quinn Karen J. , Courtney James M. 
Published: April 2007

AbstractSilicon has the ability to form polymeric chains, commonly linear chains of dimethylsiloxane, although other organic groups can be substituted for methyl. In addition, the properties of the resultant silicone polymers can vary with composition and curing procedure. This leads to a wide range of materials known as the silicones. This group of polymers, which have excellent biocompatibility, have been utilised to develop and manufacture a wide range of biomedical products. These range from simple tubing to complex implants, for example those used to replace diseased finger joints. The versatility of these materials has led to silicone products being employed in almost every medical speciality.
Interaction between polyvinylpyrrolidone and surfactant from viscosimetric data
Authors: de Sa Teresa Garcia López , Fernández Luis M. Garrido , Riaño José L. Allende 
Published: April 2007

AbstractThe intrinsic viscosities of solutions of polyvinylpyrrolidone (PVP) in water‐sodium dodecyl sulphate have been measured, for four different molecular weights of PVP, and different concentrations of sodium dodecyl sulphate at temperatures between 20 and 35°C. The exponent a of the Mark‐Houwink‐Sakurada equation has been determined, and the values of the short range interaction parameter Kθ, and expansion factor αη derived. Above a certain concentration the sodium dodecyl sulphate is adsorbed on the polymer by means of hydrophobic attractions, and the consequent repulsion between anionic heads provokes expansion of the macromolecule.
Curing kinetics of epoxy‐anhydride systems using quaternary ammonium guar and hydroxyethyl guar as catalysts
Authors: Patel Shailesh P. , Patel Ranjan G. , Patel Vithal S. 
Published: April 2007

AbstractThe kinetic parameters for the curing reactions of initially uncured and partly cured samples of the diglycidyl ether of bisphenol‐A (DGEBA) with phthalic anhydride and quaternary ammonium compounds of guar gum or quaternary ammonium compounds of hydroxyethyl guar gum as catalyst, with or without n‐butanol as diluent, were determined using the differential scanning calorimetry technique with a dynamic scan. To evaluate the kinetic parameters, four different computational methods were applied. The reaction was found to be first‐order, with activation energy in the range 65‐96 kJ mol−1.
Differential scanning calorimetric study of curing of acrylated epoxy resin with benzoyl peroxide
Authors: Thakkar Jatin R. , Patel Ranjan G. , Patel Vithal S. 
Published: April 2007

AbstractThe curing reaction of the acrylated diglycidyl ether of bisphenol‐A (DGEBA) with benzoyl peroxide has been investigated by differential scanning calorimetry at three different heating rates. The overall cure kinetics were found to be first‐order, with Arrhenius parameters E=83 kJ mol−1 and In A = 16.5 min−1, independent of the scan rate, up to at least 90% conversion.
Polymeric reagents: Part 1. Synthesis of polymer‐anchored amines useful for curing epoxy resins
Authors: Otaigbe John O. E. , Banks R. Eric , Smith Sydney 
Published: April 2007

AbstractA range of polymers carrying amino‐functions [NHEt, NHBun, NEt2, NPr, N(CH2CH2CH2NH2)2, NMeCH2CH2CH2NH2 or NEtCH2CH2CH2 NH2] has been synthesised via amination of styrene‐vinylbenzyl chloride copolymers, poly(epichlorohydrin) and poly(2‐chloroethyl vinyl ether), and via homopolymerisation and copolymerisation (with styrene) of (n‐butyl)(vinylbenzyl)‐ammonium chloride. Some of the polymers showed promise as curing agents for epoxy resins.
Synthesis and characterisation of poly(arylene sulphides): Part 10. A comparative evaluation of the thermoanalytical behaviour and curing of poly(1,4‐phenylene sulphide) and copolymers containing 1,4‐phenylene sulphide and 2‐methyl‐1,4‐phenylene sulphide repeat units
Authors: Lovell Peter A. , Still Richard H. 
Published: April 2007

AbstractThermogravimetry, differential scanning calorimetry and curing studies were used to assess the viability of random and block copolymers comprising 1,4‐phenylene sulphide and 2‐methyl‐1,4‐phenylene sulphide repeat units as alternatives to poly(1,4‐phenylene sulphide) (PPS). The properties of the copolymers are discussed critically and compared with those of the parent homopolymers PPS and poly(2‐methyl‐1,4‐phenylene sulphide) (PMPS). The results suggest that (a) random copolymers with low PMPS contents would offer the best compromise between PPS and PMPS properties, and (b) more desirable physical properties might be achieved from systems containing a less reactive 2‐substituted‐1,4‐phenylene sulphide comonomer repeat unit.
Synthesis and reactions of polytetrahydrofuran with thiolanium end groups
Authors: D'Haese François , Goethals Eric J. 
Published: April 2007

AbstractLiving polytetrahydrofuran can be terminated with thiolane to form the corresponding thiolanium‐terminated polymers. The thus obtained monotelechelic or ditelechelic polymers are unreactive towards water, but can selectively couple with charged nucleophiles by a nucleophilic ring‐opening reaction of the terminal thiolanium ions. This process has been used to prepare well‐defined homopolymers such as star polymers, segmented polymers or model networks.
Solution properties of polyelectrolytes. III. Effect of sodium polystyrene sulfonate concentration on viscometric and size exclusion chromatographic behavior at different ionic strengths
Authors: Soria Vicente , García Rosa , Campos Agustín , Braco Lorenzo , Abad Concepción 
Published: April 2007

AbstractThe effect of sodium polystyrene sulfonate concentration on the shape of its molecules in aqueous solution at different NaNO3 ionic strengths has been analyzed by viscometry and size‐exclusion chromatography (s.e.c). An equation has been developed which predicts the intrinsic viscosity, [η] p.cp.cs, at finite concentration of both polyion (cp) and electrolyte (cs). The experimental results obtained by both techniques can be accounted for in terms of the theory. Several factors involved in the elution mechanism have been considered and the variation of the slopes of s.e.c. calibration curves with cp and cs has been discussed in terms of polyion conformation changes.
Radical copolymerization of sulphur dioxide and styrene: 4. Intramolecular excimer formation in poly(styrene sulphone)s
Authors: Bae Hun‐Jai , Miyashita Tokuji , Matsuda Minoru 
Published: April 2007

AbstractIntramolecular excimer formation in poly(styrene sulphone)s with various compositions has been investigated based on the characteristic monomer sequence distributions which were determined experimentally. The fluorescence spectra of the poly(styrene sulphone)s show two emission bands at 285 nm and 330 nm as for polystyrene, corresponding to the monomer and the excimer bands, respectively. The ratio of the excimer to the monomer emission intensities (Ie/Im) is linearly correlated with the mole fraction of styrene. This observation is a consequence of the characteristic sequence distributions in poly(styrene sulphone)s. containing a very small fraction of SMS units (S = SO2; M = styrene). The efficiency of excimer formation in poly(styrene sulphone)s with regular styrene sequences, e.g. dyad sequence only, was calculated from the sequence distribution and empirical Ie/Im. It is concluded that the excimer formation in poly(styrene sulphone)s is very efficient. Energy migration along the copolymer chain was also demonstrated by measuring the degree of polarization as a function of copolymer composition. The efficient excimer formation and the depolarization in poly(styrene sulphone)s suggest that the SO2 unit in poly(styrene sulphone)s does not act as a barrier or trap to energy migration unlike the methyl methacrylate unit.
Rate and product studies in the solvolyses of methanesulfonic anhydride and a comparison with methanesulfonyl chloride solvolyses
Authors: Kevill Dennis N. , Ryu Zoon Ha , Niedermeyer Monica A. , Koyoshi Fumie , D'Souza Malcolm J. 
Published: April 2007

AbstractThe specific rates of solvolysis of methanesulfonic anhydride have been measured conductometrically at −10 °C in 41 solvents. Use of the extended Grunwald–Winstein equation, with the NT scale of solvent nucleophilicity and the YOTs scale of solvent ionizing power, leads to sensitivity to changes in solvent nucleophilicity (ℓ value) of 0.95 and a sensitivity to changes in solvent ionizing power (m value) of 0.61, with a multiple correlation coefficient (R) of 0.973. Product selectivity values (S) in binary hydroxylic solvents favor alcohol attack in EtOH–H2O (a value of 1.2 in 90% EtOH rising to 4.0 in 40% EtOH) and in MeOH–H2O (a value of 3.7 in 90% MeOH rising to 6.0 in 50% MeOH). In 2,2,2,‐trifluoroethanol–H2O, the S values are much lower at about 0.1. Entropy of activation values are appreciably negative. Literature values for the specific rates of solvolysis of methanesulfonyl chloride have been extended to fluoroalcohol‐containing solvents (titrimetric method) and, at 45.0 °C, for an overall 43 solvents values are obtained (using NT and YC1 scales) of 1.20 for ℓ and of 0.52 for m (R = 0.969). It is proposed that both substrates solvolyze by an SN2 pathway. Copyright © 2007 John Wiley & Sons, Ltd.
Investigation of ZnO substrates: effects of high temperature annealing
Authors: Graubner S. , Neumann C. , Krost A. , Bläsing J. , Meyer B. K. 
Published: April 2007

AbstractIn order to promote growth of ZnO films on ZnO substrates, defects introduced by the surface polishing procedure have to be removed. We investigate the influence of high temperature annealing in O2‐atmosphere on the structural properties of the ZnO substrates by atomic force microscopy. Only at temperatures above 1100 °C atomic steps (terraces) are seen, the remaining defects can be assigned to dislocations in a density between 104 to 105 cm–2. Interestingly the electrical properties also change from high resistive to n‐type conduction, which make the substrates – apart for the homoepitaxial growth on a perfect template – suitable for top‐to‐bottom contacts. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optical properties of anisotropic II–VI superlattices
Authors: Schillak P. , Czajkowski G. 
Published: April 2007

AbstractWe show how to compute optical spectra of semiconductor superlattices (SLs) in the region of interband electronic transitions. The method uses the microscopic calculation of superlattice minibands and the macroscopic real density matrix approach to compute the electromagnetic fields and susceptibilities. The Kronig–Penney model is adapted for computing miniband SL parameters. The electron–hole screened Coulomb potential is adapted and the valence band structure is taken into account in the cylindrical approximation, thus separating light‐ and heavy‐hole motions. We calculate the optical functions, including the optical Stokes parameters and ellipsometric functions for the case of oblique incidence. Results are given for Zn1–x Cdx Se/ZnSe SLs and a good agreement with experiments is obtained. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Post‐annealing effect upon phosphorus‐doped ZnTe homoepitaxial layers grown by MOVPE
Authors: Saito Katsuhiko , Fujimoto Kenji , Yamaguchi Kouji , Tanaka Tooru , Nishio Mitsuhiro , Guo Qixin , Ogawa Hiroshi 
Published: April 2007

AbstractThe effect of post‐annealing treatment upon the photoluminescence (PL) spectra of phosphorus‐doped ZnTe homoepitaxial layers grown by metalorganic vapour phase epitaxy using tris‐dimethylaminophosphorus (TDMAP) has been investigated. PL properties at 4 K of the layers are dramatically improved by the post‐annealing in nitrogen flow, i.e. donor–acceptor pair emission vanishes and instead free‐to‐bound transition emission (FB) and broadened acceptor‐related excitonic emission (Ia) appear. PL intensity at room temperature is enhanced remarkably by the treatment. While the post‐annealing treatment in hydrogen flow also gives an increase in PL intensity at room temperature of the layer, PL spectrum at 4 K is almost unchanged. The intensity ratio of FB to broadened Ia for the layer after post‐annealing treatment in nitrogen flow increases and the broadened Ia shifts towards longer wavelength side with increasing TDMAP transport rate. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
High temperature electrical properties of CdTe〈Pb〉 crystals under Te saturation
Authors: Fochuk P. , Grill R. , Kadys A. , Jarasiunas K. , Verstraeten D. , Feychuk P. , Parfenyuk O. , Panchuk O. 
Published: April 2007

AbstractThe point defect equilibrium of CdTe〈Pb〉 single crystals under well‐defined Te vapor pressure was investigated up to 1070 K. At 630–900 K these crystals showed p‐type conductivity and at higher temperatures – native n‐type one. During measurements the hole density reached up to ∼2 × 1017 cm–3 at 800 K. The main acceptor dominant species, which determined the electrical properties of crystals, was supposed to be the (Pb$ ^+_{\rm Cd} $V$ ^{2-}_{\rm Cd} $)– associate with its level in the gap located at EV + 0.42–0.45 eV. Above 900 K native electrons began to influence the conductivity type. Three models of point defect structure were used to describe the galvanomagnetic data – (i) frozen defect structure, (ii) defect structure with shallow or deep acceptor levels fixed during thermal cycles and native defects being in three‐phase solid–liquid–gas (SLG) equilibrium, and (iii) defect structure without any fixed energy level and defect densities being determined by the SLG equilibrium. The FWM technique confirmed p‐type photoconductivity at 300 K, but also revealed bipolar carrier generation at high photoexcitation levels with very fast electron trapping. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
In‐doped transparent and conducting cubic magnesium zinc oxide thin films grown by pulsed laser deposition
Authors: Lau C. H. , Zhuang L. , Wong K. H. 
Published: April 2007

AbstractIn‐doped n‐type semiconducting magnesium zinc oxide (MZO) thin films have been fabricated on MgO (100) and LaAlO3 (LAO) (100) substrates under low oxygen ambient by pulse laser deposition (PLD). X‐ray diffraction and HRTEM studies reveal the presence of pure cubic phase MZO (c‐MZO). High quality cube‐on‐cube epitaxy is obtained in films grown on MgO. For films deposit on LAO, they exhibit heteroepitaxial relationship of (100)c‐MZO ‖ (100)LAO and (011)c‐MZO ‖ (010)LAO. All as‐prepared c‐MZO thin films show good optical transmittance over the whole visible spectrum. Samples with In dopant concentration above 8 at% yield an electrical resistivity of less than 10–2 Ω cm and can be used as Transparent Conducing Oxide (TCO). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and properties of Zn1–x –yBex Mny Se crystals
Authors: Firszt F. , Łęgowski S. , Męczyńska H. , Rozpłoch F. , Marasek A. , Strzałkowski K. , Patyk J. , Nowak L. 
Published: April 2007

AbstractPhotoluminescence spectra, photoluminescence‐excitation spectra, Raman and EPR studies were performed in bulk Zn1–x –y Bex Mny Se solid solutions grown by the high pressure Bridgman method in the range of composition 0 < x < 0.2, 0 < y < 0.2. For low Mn content photoluminescence spectra at low temperatures consist of exciton, “edge” and deep levels emission bands. The main yellow band (2.05 eV) is due to internal transition in Mn2+. The exciton energy gap versus Mn content was determined for Zn1–x –y Bex Mny Se samples with Be content x = 0.05. EPR studies show that the g ‐factor is noticeably larger than the gfree value indicating a large exchange interaction. The decreasing of g ‐factor with increasing Mn concentration in the investigated samples can be explained as due to increasing of spin ordering. Applying the DPPH as a standard, the concentration of unpaired spins per unit weight of the crystal was estimated. Measured at room temperature Raman spectra consist of ZnSe‐like, MnSe‐like and BeSe‐like transverse (TO), longitudinal (LO), transverse (TA) and longitudinal (LA) phonon modes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Laser controlled magnetization in bulk Zn1–x Mnx Te
Authors: Khoi Le Van , Avdonin A. , Gałązka R. R. , Lentze M. , Kehl C. , Geurts J. , Eyring M. , Astakhov G. , Ossau W. 
Published: April 2007

AbstractZn1–x Mnx Te crystals (0 ≤ x ≤ 0.30) have been grown by the high pressure Bridgman technique. The free exciton energy of Zn1–x Mnx Te was determined from the photoluminescence and reflectance measurements in the temperature range from 1.7 to 270 K. The magneto‐photoluminescence and magneto‐reflectance were studied at T = 1.7 K and in magnetic fields up to 6 T. The magnetization of Zn1–x Mnx Te was calculated from the giant Zeeman effect. It was found that there is an efficient energy transfer channel from the photo‐excited carriers into the Mn2+ ions by spin‐flip scattering processes. It allows one to change the spin temperature of the Mn2+ subsystem and consequently to control its magnetization by tuning laser excitation density. The magnetization of the Zn1–x Mnx Te can be changed by 60% of its maximum value. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study of Al thermal diffusion in ZnTe using secondary ion mass spectroscopy
Authors: Tanaka Tooru , Murata Norihiro , Saito Katsuhiko , Nishio Mitsuhiro , Guo Qixin , Ogawa Hiroshi 
Published: April 2007

AbstractThe thermal diffusion of Al in ZnTe has been studied by using secondary ion mass spectroscopy. The relationships between the diffusion coefficient and the Al concentration were determined from Al depth profiles by a Boltzmann–Matano analysis. The diffusion coefficient depends on the Al concentration and it becomes large at the high doping level, probably due to the increase of Zn vacancy concentration attributed to the self‐compensation effect. As a result of decrease in the diffusion coefficient at low Al concentration, a rapid decrease in the Al concentration was observed at the diffusion front. This would lead to the formation of highly abrupt p–n junctions, resulting in the fabrication of ZnTe light emitting diode with better performance. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Local structure around Mn in Mn containing ZnO nanocrystals
Authors: Koteski V. , Zhou H. , Farangis B. , Hofmann D. M. , Meyer B. K. , Mahnke H.‐E. 
Published: April 2007

AbstractAmong the diluted magnetic semiconductors of current interest, especially ZnO is experiencing a renaissance with the incorporation of Mn because of the recent predictions from theory. We have obtained local structure information from X‐ray Absorption Spectroscopy (XAS) complementing previous electron paramagnetic resonance (EPR) studies on Mn in ZnO nanocrystals and Zn(OH)2. Mn is found to be incorporated substitutionally into the ZnO nanocrystals with a sizeable distortion as compared to the regular ZnO lattice structure. Depending on the preparation of the nanocrystals Mn is found in the ZnO core as well as in a Zn(OH)2 surface shell with a fraction which decreases upon annealing as the shell disintegrates forming additional ZnO. No indications for Mn clusters were found. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The phonon dispersion of wurtzite‐ZnO revisited
Authors: Serrano J. , Manjón F. J. , Romero A. H. , Ivanov A. , Lauck R. , Cardona M. , Krisch M. 
Published: April 2007

AbstractInelastic neutron scattering measurements are reported for the optical phonon branches of wurtzite ZnO. The experimental data are in excellent agreement with the ab‐initio calculations for the phonon dispersion relations based on linear response theory. Discrepancies between theory and present data observed for the longitudinal optic branches along the [100] and [001] directions are attributed to an inaccurate description of the dielectric constant of ZnO and, consequently, the crystal‐ and electric‐field splitting. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)