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  • 1
    Electronic Resource
    Electronic Resource
    Kinetic study and crosslink density in styrenebutadiene rubber compounds filled with boron-amine-modified silica (1995)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 227 (1995), S. 43-55 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Kinetik der Vulkanisation sowie die Vernetzungsdichte von Styrol-Butadien-Kautschukmischungen wurden mit zwei Vulkanisationssystemen, einem wirksamen (EV) und einem konventionellen (CV), untersucht. Ein oberflächenmodifiziertes Silikat mit Boramingruppen (Si—O—B—(NH2)2) wurde als Füllstoff eingesetzt. Unbehandeltes und mit zwei Silanen (γ-Mercaptopropyl-trimethoxysilan und γ-Aminopropyl-triethoxysilan) modifiziertes Silikat wurden zum Vergleich eingesetzt. Die bestenkinetischen Parameter, wie die höchste Vulkanisierungsgeschwindigkeit, die längste Induktionszeit und die kleinste Aktivierungsenergie, wurden für die Mischung mit boraminiertem Silikat erhalten. Die Vernetzungsdichte, die mit dieser Mischung erreicht wurde, ist ähnlich der von mit Silan modifiziertem Silikat erzielten, da wahrscheinlich die Boramingruppen auf der Silikatoberfläche besser verteilt sind. Diese Fakten führen zu wichtigen technologischen Verbesserungen: größere Verarbeitungssicherheit, schnellere Vulkanisierungsgeschwindigkeit und verbesserte physikalische Eigenschaften.
    Notes: Vulcanization kinetics and crosslink density of styrene-butadiene rubber compounds have been studied with two vulcanization systems, an efficient (EV) and a conventional (CV) one. A surface-modified silica with boron-amine groups (Si—O—B—(NH2)2) was employed as filler. Untreated and modified silica with two silanes (γ-mercaptopropyl-trimethoxysilane and γ-aminopropyl-triethoxysilane) have been used as reference.The best kinetic parameters, such as highest vulcanization rate, longest induction time and lowest activation energy, were obtained for the compound with boronaminated silica. The crosslink density, achieved with this compound, is similar to that with silane-modified silica, probably because of the better surface distribution of boron-amine groups on the silica. These facts lead to important technological improvements: better processing safety, faster vulcanization rate and improved physical properties.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1995.052270106
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  • 2
    Electronic Resource
    Electronic Resource
    Behaviour of a silica filler surface-modified with boron-amine groups (1994)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 217 (1994), S. 107-117 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Das Verhalten von mit primären Boramingruppen modifizierten Silikat-Füllstoffen wurde unter verschiedenen Reaktionsbedingungen untersucht. Der Füllstoff mit den besten Verstärkungseigenschaften wurde eingesetzt, um zwei unterschiedliche Vulkanisationssysteme zu vergleichen: ein wirksames Vulkanisationsverfahren (EV), das nach ISO als Methode zur Untersuchung des Verstärkungsverhaltens neuer Silikate empfohlen wird, sowie ein konventionelles Verfahren. Die besten Ergebnisse werden mit Silikat erhalten, welches 3 h bei 500°C behandelt wurde; unter diesen Bedingungen werden die meisten der primären Boramingruppen fixiert. Die Eigenschaften des nach dem EV-Verfahren modifizierten Silikats ähneln denen von mit Silan modifizierten Silikaten und sind in einigen Fallen besser als jene, welche nach dem konventionellen Verfahren erhalten werden. In allen Fallen wird die verstarkende Wirkung von gefällten Silikat-Füllstoffen durch die Boraminbehandlung verbessert.
    Notes: The behaviour of silica fillers modified with primary boron-amine groups has been studied under different reaction conditions. The filler with the best reinforcing properties was used to compare two different vulcanization systems: an efficient vulcanization system, EV, which is the recommended ISO Standards method to study the reinforcing behaviour of new silicas, and a conventional vulcanization system.The results indicate that the best properties are obtained with silica treated for 3 h at 500°C, reaction conditions which fix most of the primary boron-amine groups. Using the EV system, the properties of this modified silica are similar to those of silane-modified silica, and in some cases better than those obtained with a conventional vulcanization system. In all cases, the boron-amination treatment significantly improves the behaviour of precipitated silica as a reinforcing filler.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1994.052170111
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  • 3
    Electronic Resource
    Electronic Resource
    The system poly(4-hydroxystyrene)/poly(vinyl acetate)/acetone: An experimental and theoretical study (1994)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 195 (1994), S. 1043-1062 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: In an effort to assess the intermolecular interactions between poly(4-hydroxystyrene)IUPAC name: poly(4-vinylphenol). (P4HS) and poly(vinyl acetate) (PVAc), two types of experimental measurements were conducted: volumetric properties and vapor pressures of solutions in a common solvent (probe). The PVT measurements for a 50:50 (w/w) binary polymer mixtures were conducted over a pressure range from 0 to 100 MPa and a temperature range from 350 to 470 K. The vapor pressures of acetone over a series of ternary systems acetone/P4HS/PVAc, and for four intermediate weight ratios PVAc/P4HS, were measured at 298,15 K, 308,15 K and 318,15 K. PVAc and P4HS interact primarily through hydrogen bonding. The probe molecule (acetone) on the other hand interacts also through hydrogen bonding with P4HS. A recent equation-of-state theory of hydrogen bonding has been used to correlate these measurements. Application of the theory was requiring the knowledge of the volumetric behavior of pure P4HS. Extensive PVT measurements for this polymer have also been conducted. The PVT measurements for the polymer mixture were used in order to estimate the hydrogen bonding parameters for the hydroxyl-ester pair. The vapor pressures of the system acetone/P4HS were used in order to estimate the hydrogen bonding parameters of the hydroxyl-carbonyl pair. On the basis of this information the theory was used to predict the vapour pressures of the ternary system. The theoretical predictions are in quantitative agreement with the experiments.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1994.021950320
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  • 4
    Electronic Resource
    Electronic Resource
    Tensions superficielles de copolymères méthacryliques perfluoroalkylés (1995)
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 196 (1995), S. 1063-1075 
    Details
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The surface properties of methacrylic copolymers with a random distribution of perfluoroalkyl pendent groups were studied by a tensiometric method and were found to depend on the concentration of fluorinated units (2-hydroxy-4,4,5,5,6,6,7,7,8,8,9,9,9-tridecafluorononyl methacrylate (1)), and the nature of the non-fluorinated methacrylic ester (methyl, butyl, stearyl). The surface tensions estimated by various approaches (critical surface tension, geometric and harmonic mean approximations) are very low (11 mN · m-1 〈 y 〈 12 mN · m-1). The surface tension of the copolymers drops drastically when a few percent of fluorinated units are incorporated into the polymeric chain. The wetting hysteresis, observed particularly in the case of water, could be due to the mobility of macromolecular chains at the interface, leading to a reorganization of fluorinated groups in order to minimize the interfacial energy.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/macp.1995.021960409
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  • 5
    Electronic Resource
    Electronic Resource
    Using full-CI algorithms in Bethe-Goldstone-type expansions of the correlation energy (1997)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 61 (1997), S. 35-43 
    Details
    ISSN: 0020-7608
    Keywords: Chemistry ; Theoretical, Physical and Computational Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the early 1960s, Nesbet proposed to develop correlation energy in terms of two-, three-, four-, etc., electron contributions. This expansion was, in principle, applicable to a large number of electrons without a size-extensivity error. The now available full-CI algorithms may be used to obtain those expansions in terms of either occupied spin - orbitals or, more efficiently, in terms of sets of occupied or virtual molecular orbitals. Tests on the NH3 molecule with a DZP basis-set problem show the slow convergence of this approach. © 1997 John Wiley & Sons, Inc.
    Additional Material: 6 Tab.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Nonlocal exchange and kinetic-energy density functionals for electronic systems (1992)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 44 (1992), S. 347-358 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nonlocal weighted density approximation (WDA) to the exchange and kinetic-energy functionals of many electron systems proposed several years ago by Alonso and Girifalco is used to compute, within the framework of density functional theory, the ground-state electronic density and total energy of noble gas atoms and of neutral jellium-like sodium clusters containing up to 500 atoms. These results are compared with analogous calculations using the well known Thomas-Fermi-Weizsäcker-Dirac (TFWD) approximations for the kinetic (TFW) and exchange (D) energy density functionals. An outstanding improvement of the total and exchange energies, of the density at the nucleus and of the 〈r-1〉 expectation values is obtained for atoms within the WDA scheme. For sodium clusters we notice a sizeable contribution of the nonlocal effects to the total energy and to the density profiles. In the limit of very large clusters these effects should affect the surface energy of the bulk metal. © 1992 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560440830
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  • 7
    Electronic Resource
    Electronic Resource
    Ionization potentials of atoms calculated with a nonlocal exchange and a local correlation functional (1994)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 52 (1994), S. 993-1010 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We calculate the first ionization potential of atoms (3 ≤ Z ≤ 54) by means of a nonlocal density functional approach and the results are compared with those obtained using other recent density functional approaches based on density gradients. In these calculations, we use a nonlocal weighted spin-density approximation of exchange effects and a local spin-density approximation of Coulomb correlation, both based on novel forms of the pair-correlation functions. We also calculate the total energies of the He, Be, and Ne isoelectronic series. © 1994 John Wiley & Sons, Inc.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560520425
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  • 8
    Electronic Resource
    Electronic Resource
    Nonlocal functionals for exchange and correlation in density functional theory: Application to atoms and to small atomic clusters (1995)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 56 (1995), S. 499-508 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The local density approximation (LDA) to exchange and correlation effects has well-known limitations. The nonlocal weighted density approximation (WDA) corrects some of those defects. This is illustrated here by applications to free atoms and small atomic clusters. The WDA also induces a nonlocal kinetic energy functional that is tested for atoms. © 1995 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560560508
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  • 9
    Electronic Resource
    Electronic Resource
    A study of coronene - coronene association using atom - atom pair potentials (1996)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 57 (1996), S. 567-573 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study of the coronene - coronene association using different interaction potentials based on an atom-atom pair potential proposed by Fraga has been performed. The interaction potentials employed differ in the way the electrostatic and/or dispersion contributions are computed. The influence of both contributions on the geometries predicted for the coronene dimer is discussed in order to analyze the effectiveness of the different interaction potentials. The stationary points found in each interaction energy hypersurface are characterized by calculating the Hessian eigenvalues. Results are discussed in the light of those previously reported for the benzene dimer. Stacked-displaced structures are suggested to be the preferred conformations for the coronene - coronene association. © 1996 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    Nonlocal approximation to the exchange and kinetic energy functionals: Application to metallic clusters (1993)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 45 (1993), S. 333-347 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The nonlocal weighted density approximation (WDA) to the exchange and kinetic energy functionals of many-electron systems proposed several years ago by Alonso and Girifalco in the context of density functional theory is used to compute, within the framework of the spherical jellium model, the ground-state electronic density, chemical potential, and total energy of neutral and negatively and positively charged sodium clusters containing up to N = 800 atoms. From these calculations, we study the behavior of the total energies per atom, chemical potentials, ionization potentials, I(N), and electron affinities, A(N). These results are compared with analogous calculations using the well-known Thomas-Fermi-Weizsäcker-Dirac (TFWD) approximation for the kinetic (TFW) and exchange (D) energy functionals. Calculations including the local density approximation (LDA) to the correlation energy in both WDA and TFWD functionals are also presented. © 1993 John Wiley & Sons, Inc.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560450402
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