bluuebunny/crossref_metadata_2025_split huggingface dataset:
Elasticity of hexagonal liquid crystals
Authors: Derbel N , Raïs K , Tounsi N , Othman T , Gharbia M , Gharbi A , Nguyen H T , Malthête J 
Published: September 2002

AbstractAn investigation of the elastic properties of hexagonal phases of typical liquid crystal samples on an ordered hexagonal discotic hexa‐n‐octyloxytriphenylene (C8HET), a disordered one a triphenylene hexa‐n‐dodecanoate (C11HAT) and a hexacatenar phasmid was carried out. Characterization of their mechanical stability and analysis of light scattering were used; the same results were obtained for the three samples in spite of the differences in their molecular shapes and molecular orders in columns. From the instability of undulating columns submitted to a dilative strain normal to columns, we deduced an anomalously large value of the correlation lengthm(m ≈ 0.1 µm), compared to that of the smectic liquid crystals (m ≈ 20 Å). Results from depolarized Rayleigh scattering showed that, although consisting of one‐dimensional liquid‐like structures, the studied samples in their hexagonal phases behaved elastically like three‐dimensional solids. Considering the differences in molecular shapes and orders, this elastic behaviour was attributed to regular defects. Therefore, one can probably generalize this elastic behaviour as being due to the columnar hexagonal structure.© 2001 Society of Chemical Industry
Relation between microstructure and glass transition temperature of poly[(methyl methacrylate)‐co‐(ethyl acrylate)]
Authors: Nguyen Giao , Nicole Daniel , Matlengiewicz Marek , Roizard Denis , Henzel Norbert 
Published: September 2002

AbstractThe glass transition temperature of a series of samples of the poly[(methyl methacrylate)‐co‐(ethyl acrylate)] copolymer, synthesized at low conversion, were calculated theoretically using the equations of Barton and Johnston. The values obtained are more precise when the probabilities of the compositional diads are derived from the 13C NMR data instead of the classical method utilizing reactivity ratios. This can be observed more clearly when the copolymer samples are synthesized at high conversion. Introduction of configuration (tacticity) at the diad level confirms the above observations and slightly improves the calculated values of Tg compared to the initial formulae which were only taking into account the compositional sequences of the copolymer.© 2001 Society of Chemical Industry
Influence of heat treatment on the space charge within an epoxy resin polymer material
Authors: Guermazi Hajer , Smaoui Hichem , Agnel Serge , Mlik Youssef , Toureille Alain , Schué François 
Published: September 2002

AbstractThe influence of heat treatment on the appearance and the evolution of the space charge repartition within an epoxy resin polymer material is investigated. The space charge measurements were made using the thermal step method (TSM) and the thermally stimulated depolarization currents (TSDC) method. The results obtained show the behaviour of the space charge density after heat treatment and, in particular, it can be concluded that the charges are stabilized in deep levels.© 2001 Society of Chemical Industry
Synthesis and characterization of poly(ether ketone ketone) (PEKK)/sodium sulfonated poly(arylene ether ketone) (S‐PAEK) block copolymers
Authors: Gan Daoji , Lu Shiqiang , Wang Zhijian 
Published: September 2002

AbstractA series of well‐defined poly(ether ketone ketone) (PEKK)/sodium sulfonated poly(aryl ether ketone) (S‐PAEK) block copolymers of high molecular weights was prepared by direct nucleophilic polymerization of hydroquinone with sodium 5,5′‐carbonylbis(2‐fluorobenzene sulfonate) (1) and PEKK oligomer (2). Varying the ratio of 1 to 2 used in polymerization can be used to control the degree of polymer sulfonation, which correspondingly affects the polymer solubility in solvents. Increasing content of 1 in the copolymers, slightly decreases their thermal stability which is nevertheless thermally stable up to 400 °C. Two Tg values, or one broad Tg, were observed in the DSC measurements of the block copolymers, indicating the existence of phase separation, which was further proved by phase‐separated morphologies as shown in atomic force microscopy images.© 2001 Society of Chemical Industry
Influence of temperature on lattice spacings of melt‐crystallized poly(iminosebacoyl iminodecamethylene)
Authors: Yang Xiaoniu , Kong Xiaohua , Tan Susheng , Li Gao , Zhou Enle 
Published: September 2002

AbstractThe variation of lattice spacings of poly(iminosebacoyl iminodecamethylene) (nylon‐10,10) with temperature was studied by wide‐angle X‐ray diffraction (WAXD) during both heating and cooling processes, which demonstrates a gradual and continuous transition with temperature. However, the crystal melts before the two peaks merge completely. Both WAXD and differential scanning calorimetry show that crystallization from molten sample results directly in the triclinic form. Additionally, this transition is thermodynamically reversible.Comparison of this transition with that of nylon‐6,6, suggests that no hydrogen‐bonded network is formed during or after the transition. We prefer to attribute this transition to asymmetrical thermal expansion in the nylon‐10,10 crystals rather than to a true first‐order phase transition.© 2001 Society of Chemical Industry
Experimental testing of a random medium optical model of porous silicon for photovoltaic applications
Authors: Abouelsaood A. A. , Ghannam M. Y. , Stalmans L. , Poortmans J. , Nijs J. F. 
Published: September 2002

AbstractWe have developed a model for light propagation in porous silicon (PS) based on the theory of wave propagation in random media. The low porosity case is considered, with silicon being the host material assuming randomly distributed spherical voids as scattering particles. The specular and the diffuse part of the light could be determined and treated separately. The model is applied to the case in which porous silicon would be used as a diffuse back reflector in a thin‐film crystalline silicon solar cell realized in an ultrathin (1–3 μm) epitaxially grown Si layer on PS. Three layer structures (epi/PS/Si) have been fabricated by atmospheric pressure chemical vapor deposition (APCVD) of 150–1000 nm epitaxial silicon layers on silicon wafers of which 150–450 nm of the surface has been electrochemically etched. An excellent agreement is found between the experimentally measured reflection data in the 400–1000 nm wavelength range and those calculated using the proposed model. The values of the layer thickness agree, within a reasonable experimental error, with those obtained independently by cross sectional transmission electron microscopy (XTEM) analysis. This provides an experimental verification of the random medium approach to porous silicon in the low porosity case. The analysis shows that the epitaxial growth process has led to appreciable porosity decrease of an initially high porosity layer from about 60% to 20–30%. Copyright © 2001 John Wiley & Sons, Ltd.
Measures used to protect people exposed to a PV generator: ‘univer project’
Authors: Vidal P. G. , Almonacid G. , Pérez P. J. , Aguilera J. 
Published: September 2002

AbstractMany of the solutions to integrate PV in buildings have the special feature of placing the generator in transit areas where people can have access to inside zones of the installation (metalworks, modules, junction boxes, etc.). In these cases, if we also need a higher level of generation voltage, due to the generator size and efficiency reasons, the risk of electrical damage to people rises due to imprudences or installation faults. In this paper, we present a system of people protection designed and installed in a PV generator integrated in a parking and building area at Jaén University Campus. This PV generator has a high risk level of electric shock to humans due to its location and voltage generator level (range 500 VDC). We include both the theoretical design of the protection subsystem and also the experimental tests and measures to check its functionality and security level reached in the installation. Copyright © 2001 John Wiley & Sons, Ltd.
Solar cell efficiency tables (version 17)
Authors: Green Martin A. , Emery Keith , King David L. , Igari Sanekazu , Warta Wilhelm 
Published: September 2002

AbstractConsolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined and new entries since July 2000 are reviewed. Copyright © 2001 John Wiley & Sons, Ltd.
The effect of oxygen on interface microstructure evolution in CdS/CdTe solar cells
Authors: Albin D.S. , Yan Y. , Al‐Jassim M.M. 
Published: September 2002

AbstractMicrostructural changes at the CdS/CdTe solar cell interface where close‐spaced sublimation (CSS) is used as the growth technique to deposit thep‐type CdTe absorber layer are studied by systematic layer characterization at various stages during heterojunction growth. CdS layers grown by both chemical bath deposition (CBD) and CSS provide a basis for determining the effects of CdS crystallinity, grain size, and oxygen content on the subsequent CdTe layer. As‐grown CBD CdS films exhibit small grains and variations in optical properties attributed to film impurities. In contrast, CSS yields CdS films with good crystallinity, larger grains, and nearly ideal optical properties. The hexagonal nature of CSS‐grown CdS is seen to nucleate hexagonal CdTe during the initial stages of CdTe film growth. Cubic CdS deposited by CBD in contrast promotes cubic CdTe nucleation. Oxygen anneals in the latter case can aid hexagonal CdTe nucleation. Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) of the CdS/CdTe interface show CdS‐dependent differences in interdiffusion at the interface. This interdiffusion appears to be determined by the oxygen level in the CdS. When low‐oxygen‐containing CSS CdS films are used, sulfur diffusion is substantial, leading to significant consumption of the CdS layer. When these same films are annealed in oxygen, the consumption is reduced. Te diffusion into the CdS layer is also observed to decrease with oxygen anneals. Optical modeling shows that Te alloying with the CdS layer can greatly reduce the short‐circuit current of CdS/CdTe devices. Copyright © 2002 John Wiley & Sons, Ltd.
Solar Cell Efficiency Tables (Version 20)
Authors: Green Martin A. , Emery Keith , King David L. , Igari Sanekazu , Warta Wilhelm 
Published: September 2002

AbstractConsolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined and new entries since January, 2002 are reviewed. Copyright © 2002 John Wiley & Sons, Ltd.
Possible effects on the polyethene chain structure of trimethylaluminum coordination to zirconocene catalysts
Authors: Liu Jianke , Støvneng Jon Andreas , Rytter Erling 
Published: September 2002

AbstractEthene was polymerized with the catalytic systems L2ZrCl2/MAO/TMA (where L = Cp, Me5Cp, or Me4Cp; Cp = η5‐cyclopentadienyl; MAO = methylaluminoxane; and TMA = trimethylaluminum) at 60 °C, 2 bar, and AlTMA/Zr ratios of 0–2700. The polymerization activity was reduced with the addition of TMA for L = Cp but was almost unaffected for the methyl‐substituted catalysts. Increasing the TMA concentration resulted in a lower molecular weight of the polymer, with the largest effect for L = Me5Cp. A gel permeation chromatography analysis of the polymers revealed a high molecular weight shoulder and a nearly bimodal distribution for L = Me5Cp at high TMA concentrations. A possible explanation of such a shoulder in terms of long‐chain branching was ruled out by dynamic viscosity measurements. The origin of this effect more likely stemmed from competition between chain transfer to aluminum and β‐hydrogen transfer reactions at two different sites, one TMA‐sensitive and one TMA‐insensitive. Polymerizations at various pressures and temperatures substantiated this assumption. A clue to the underlying mechanism came from investigations of chain transfer to TMA studied with density functional calculations. Complexation of Me3Al to Zr was much stronger for L = Cp than for L = Me5Cp. However, the overall chain‐transfer barrier was much higher for L = Cp. These results agreed both with the reduced activity for L = Cp and with the strongly reduced molecular weight for L = Me5Cp observed with the addition of TMA. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3566–3577, 2001
Synthesis and characterization of novel polyimides containing stilbene unit in the side chain and their controllability of nematic liquid crystal alignment on the rubbed surfaces
Authors: Park J. H. , Jung J. C. , Sohn B.‐H. , Lee S. W. , Ree M. 
Published: September 2002

AbstractFour polyimides containing hexylene spacer and a fluorostilbene unit in the side chains were prepared in thin‐film form by two‐step condensation of 3,3′‐bis[(4′‐fluoro‐4‐stilbenyl)oxyhexyloxy]‐4,4′‐biphenyldiamine (FS6B) with pyromellitic dianhydride (PMDA), benzophenone‐3,3′,4,4′‐tetracarboxylic dianydride (BTDA), 4,4′‐oxydi(phthalic anhydride) (ODPA), and 4,4′‐hexafluoroisopropylidenedi(phthalic anhydride) (6FDA), respectively, and their controllability of liquid crystal (LC) alignment on rubbed surfaces was investigated. Pretilt angles of LCs were achieved in the 2–9° range, depending on the rubbing density and backbone structures. The effect of the mesogenic stilbene group on the pretilting of LCs was distinctive in FS6B‐PMDA. Contact‐angle measurements on thin films annealed at 120 °C revealed that FS6B‐PMDA potentially had the better alignment stability than FS6B‐6FDA. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3622–3632, 2001
Synthesis and properties of oxygen‐, methylene‐, and alkylene‐bridged poly(dithiafulvene)s
Authors: Marathe Sujata , Uemura Takashi , Naka Kensuke , Chujo Yoshiki 
Published: September 2002

AbstractPolymerization by cycloaddition between aldothioketene and its alkynethiol tautomer (derived in situ from a diyne) leading to the formation of dithiafulvene unit‐linked polymers has been studied. Two aromatic diynes [bis(4‐ethynyldiphenyl)methane (1a) and 4,4′‐diethynyldiphenyl ether) (1b)] were used as starting materials with the aim of obtaining non‐π‐conjugated methylene‐ and oxygen‐bridged aromatic poly(dithiafulvene)s. The poly(dithiafulvene) derived from bis(4‐ethynyldiphenyl)methane can be considered as an interesting precursor to a small band‐gap polymer having alternating aromatic and quinonoid moieties. Further, two aliphatic diynes [1,7‐octadiyne (3a) and 1,9‐decadiyne (3b)] were subjected to cycloaddition polymerization to obtain aliphatic poly(dithiafulvene)s containing localized electron‐rich dithiafulvene units. The polymers obtained were characterized by IR, 1H NMR, gel permeation chromatography, and cyclic voltammetry. The electron‐donating property of the polymers was evident from the charge‐transfer (CT) complex formation with an electron acceptor 7,7,8,8‐teracyanoquinodimethane. The CT complexes were characterized by IR, 1H NMR, and ultraviolet–visible spectroscopies. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3593–3603, 2001
Synthesis of epoxy monomers that undergo synergistic photopolymerization by a radical‐induced cationic mechanism
Authors: Crivello James V. , Ortiz Ricardo Acosta 
Published: September 2002

AbstractA series of novel, cycloaliphatic, cationically photopolymerizable epoxide monomers bearing benzyl ether groups were prepared. These monomers display a considerable enhancement in the rate of their cationic ring‐opening polymerizations in comparison with monomers that do not contain such groups. In this article, a synergistic free‐radical mechanism is proposed that accounts for this effect, and supporting evidence is offered for its verification. During UV irradiation of an onium salt cationic photoinitiator, the aryl radicals that are generated abstract labile benzyl hydrogens present in such monomers to generate the corresponding carbon‐centered radicals. Subsequently, these radicals are oxidized to benzyl carbocations by the onium salt via a nonphotochemical chain process. The observed increase in the rate and extent of the cationic ring‐opening polymerization of the epoxide monomers is due to the aforementioned mechanism, which effectively increases the number of reactive cationic species present during polymerization. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3578–3592, 2001
Preparation of monolithic polymers with controlled porous properties for microfluidic chip applications using photoinitiated free‐radical polymerization
Authors: Yu Cong , Xu Mingcheng , Svec Frantisek , Fréchet Jean M. J. 
Published: September 2002

AbstractA broad variety of monolithic macroporous polymers with both controlled chemistry and porous properties was prepared using UV‐initiated free‐radical polymerization. The chemistry of the monoliths is defined by the composition of the monomer mixture used for the polymerization. The use of functional methacrylate monomers such as glycidyl methacrylate, 2‐hydroxyethyl methacrylate, butyl methacrylate, 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid, and [2‐(methacryloyloxy) ethyl] trimethylammonium chloride enabled the preparation of monoliths with reactive, hydrophilic, hydrophobic, and ionizable functionalities, respectively. The porous properties of these monoliths were mainly affected by the choice of the porogenic solvent system. Because the UV polymerization was carried out at room temperature, even low molecular weight alcohols and other low boiling point solvents could safely be used to create a versatile series of binary porogenic mixtures. Monoliths were prepared in spatially defined positions using the photolithographic technique within a fused silica capillary and on microfluidic chips, and the former was demonstrated with the separation of derivatized amines by means of capillary electrochromatography in the reversed‐phase mode. Similarly, a monolith prepared in the microchip format was used to demonstrate a microextraction with enrichment of a solution of green fluorescent protein by a factor of 1000. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 755–769, 2002; DOI 10.1002/pola.10155
Complex formation of polyethyleneimine with copper(II), nickel(II), and cobalt(II) ions
Authors: Kislenko V. N. , Oliynyk L. P. 
Published: September 2002

AbstractAn influence of the structure of a globule of polyethyleneimine on the complex formation of one with the copper(II), nickel(II), and cobalt(II) ions is described. A change of the coordination number from the pH of solution for complexes of ethylenediamine, diethylenetriamine, and polyethyleneimine with metal ions was found. The fraction of monomer links, bound with metal ions, depends on the volume of the globule of macromolecule as well as the condition of the proceeding reaction. The reaction of complex formation is controlled by the diffusion of metal ions into the polymer globule in solution. The effective equilibrium constants of complex formation were found. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 914–922, 2002; DOI 10.1002/pola.10157
New synthetic method for aromatic polyketones from bis(arylsilane)s and aromatic dicarboxylic acid chlorides
Authors: Takeuchi Hisashi , Kakimoto Masa‐aki , Imai Yoshio 
Published: September 2002

AbstractA new synthetic method for aromatic polyketones was developed through Friedel–Crafts polycondensation of bis(arylsilane) monomers with aromatic dicarboxylic acid chlorides. The solution polycondensation of these monomer pairs in the presence of aluminum chloride in 1,2‐dichloroethane readily afforded aromatic polyketones having inherent viscosities up to 0.37 dL/g with the elimination of chlorotrimethylsilane. The polycondensation proceeded through aromatic electrophilic ipso substitution, the mechanism of which is very similar to that of normal Friedel–Crafts acylation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2729–2735, 2002
Kinetic study of the stable free‐radical copolymerization of styrene with butyl methacrylate
Authors: Cuervo‐Rodriguez Rocio , Fernández‐Monreal Carmen , Madruga Enrique López 
Published: September 2002

AbstractThe radical copolymerization of styrene and n‐butyl methacrylate mediated by 1‐phenyl‐1‐(2′,2′,6′,6′‐tetramethyl‐1′‐piperidinyl‐oxy)ethane in bulk at 125 °C has been analyzed over a wide range of conversions and monomer feed compositions. Monomer reactivity ratios have been determined, and the Mayo–Lewis terminal model provides excellent predictions for the variations of the intermolecular structure over the entire conversion range. The kinetic analysis of this copolymerization system indicates an apparent propagation rate coefficient independent of the monomer feed composition as well as a limiting conversion that decreases as the styrene monomer feed decreases. This fact is attributed to side reactions leading to unsaturated end groups and the accumulation of nonactive adducts of n‐butyl methacrylate. The number‐average molecular weights linearly increase with conversion, and the copolymers present narrow molecular weight distributions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2750–2758, 2002
Influence of the amine structure on the polymerization of methyl methacrylate photoinitiated by aromatic ketone/amine
Authors: Valderas C. , Bertolotti S. , Previtali C. M. , Encinas M. V. 
Published: September 2002

AbstractThe polymerization of methyl methacrylate photoinitiated by 2‐chlorothioxanthone in the presence of amines of different structures has been investigated. The photoinitiation efficiency of these systems is highly dependent on the structure of the amine. The polymerization rate increases with the amine concentration, reaching a constant value in an amine concentration range of 10–30 mM. At these amine concentrations, aliphatic hydroxyalkyl amines are more efficient photoinitiators than the corresponding alkyl‐substituted compounds. Dimethylanilines with electron‐acceptor substituents in the 4‐position give higher polymerization rates than electron‐donor‐substituted anilines. The photophysics of these photoinitiation systems has been studied in the polymerization medium. These data show that the singlet and triplet excited states of thioxanthones are efficiently deactivated by the amine. Rate constants are well correlated to the oxidation potential of the amine. These studies have allowed us to simulate the dependence of the photoinitiation efficiency with the amine concentration and indicate that the active radicals are produced from the interaction of the ketone triplet with the amine. Also, photochemical studies have allowed us to establish that the dependence of the polymerization rate on structural features of amines is mainly due to differences in the fraction of produced active radicals that add to the monomer. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2888–2893, 2002