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  • Polymer and Materials Science  (13)
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  • 1
    Electronic Resource
    Electronic Resource
    Influence of a neutral surface on polymer molecules in the vicinity of the surface (1989)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 27 (1989), S. 655-671 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Monte Carlo simulations based on the rotational isomeric model are used to investigate the influence of a neutral surface on the structural and thermodynamic descriptors of polymethylene chains on and in the vicinity of the surface. For large chains, the results of the simulations are replicated by a properly scaled distribution based on a random walk with absorbing barriers. Accordingly, the affects noted for the trial polymethylene system may be extended to other molecules.The perturbations in the geometry of the chain were confined to the components of the various descriptors perpendicular to the surface; the radial components were unaffected by the neutral surfaces. The perturbations induced by the neutral surfaces extend to chains whose origins were within about $\[ 10\left\langle {s_x \left( \infty \right)^2 } \right\rangle ^{1/2} \]$, where $\[ \left\langle {s_x \left( \infty \right)^2 } \right\rangle ^{1/2} \]$ is the perpendicular component of the mean square radius of gyration of an unperturbed chain.In contrast, the average bond conformation, the associated internal energy, and the variance of the internal energy distribution are unaffected by a neutral surface. The major thermodynamic effect is manifest through the entropy arising from the reductions in accessible chain configurations due to the neutral barrier.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1989.090270312
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  • 2
    Electronic Resource
    Electronic Resource
    Deformation mechanisms of constrained polymer chains. I. Geometrically induced correlations in the deformation response mechanisms of tie molecules (1977)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 15 (1977), S. 1805-1835 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The geometrical constraints acting on sections of tie molecules in noncrystalline regions severely limit the number and type of available polymer chain conformations. It is shown that these constraints induce explicit correlations in the rotations about the backbone bonds. These correlated rotations, in turn, specify distinct structural conversion paths which define the molecular mechanisms underlying the deformation response of tie molecules. Application of these constraining relationships to highly oriented polyethylene shows that the kink and jog structures of tie molecules can be decomposed into combinations of three primary conformational building blocks. Each of the basic conformational subunits follow an explicit set of dihedral angle correlations and, consequently, imparts specific characteristics to the composite structure of tie molecules. It is proposed that the composite response characteristics of tie molecules can be described as linear combinations of the response characteristics of these three primary conformational subunits.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1977.180151010
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  • 3
    Electronic Resource
    Electronic Resource
    Deformation mechanisms of constrained polymer chains. II. Deformation energetics of tie molecules (1977)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 15 (1977), S. 1837-1861 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Energy-deformation characteristics for the primary T, S, and U conformational units of tie molecules were obtained from the analysis of data generated from a constrained minimization algorithm. Energy-deformation profiles (covering the range from compact equilibrium defect structures to the fully extended chain) are reported for the S0 and S1 members of the Sλ family and for the U00 member of the Umn family. Estimates of the energy content V0 and the elastic modulus E were obtained from the computed energy-deformation data in the vicinity of the equilibrium Structure - S0 → {60°, 180°, -60°}, V0S0 = 1.7 kcal/mole, ES0 = 60 kcal/cm3 [250 × 1010 dyn/cm2];S1 → {60°, 180°, 180°, 180°, -60°}: V0S0 = 1.7 kcal/mole, ES1 = 25 kcal/cm3 [100 × 1010 dyn/cm2]; and U00 → {60°, 180°, 60°, 180°, 60°}: V0U00 = 2.7 kcal/mole, EU00 = 80 kcal/cm3 [340 × 1010 dyn/cm2]. Although the elastic modulus of the U00 unit is comparable to the elastic modulus of the fully extended chain, the highenergy content of this unit (V0 = 2.7 Kcal/mole) prohibits a significant population and thereby mitigates an appreciable reinforcing effect from this rigid unit. A model for a surrogate force constant is introduced to generalize the results from this study to any member of the Sλ or Umn family as well as any combination of Sλ and Umn units. This generalization provides a basis for estimating the deformation characteristics of tie molecules comprised of various populations of these primary conformational building blocks.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1977.180151011
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  • 4
    Electronic Resource
    Electronic Resource
    Energetics of phase transformations in polyethylene (1973)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 11 (1973), S. 1385-1411 
    Details
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The molecular mechanisms involved in the orthorhombic-to-monoclinic phase transformation in polyethylene were investigated by the computer simulation of a structure-energy map based on empirically justified intermolecular potential functions. Stable packing structures for the orthorhombic and monoclinic form were isolated as relative minima, cohesive energies were determined from the energy minima, specific chain motions involved in the transformation were identified by the minimum energy path connecting the packing minima, and the activation energy for the transformation was determined from the energy barrier along the minimum energy transformation path. The packing structure parameters predicted from the energy map were in excellent agreement with unit cell dimensions observed near 0°K. The activation energy predicted for the transformation is relatively low (∼0.5 kcal/mole of ethylene at 0°K and 0.25 kcal/mole of ethylene near the melting point, 411°K). Monoclinic packing was predicted to be slightly more stable than orthorhombic. Since this result is inconsistent with a large body of observations, we propose that the intramolecular energy of chain folds plays a dominant role in establishing chain-packing geometry. The inclusion of fold-transition energetics could give rise to transformation mechanisms which differ in details from those proposed in this work.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1973.180110713
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  • 5
    Electronic Resource
    Electronic Resource
    Measurement of diffusivity of a liquid diamine in solid epoxies using attenuated total reflectance infrared spectroscopy (FTIR-ATR) (1994)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 52 (1994), S. 1241-1248 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A number of studies on thermosetting polymeric composite materials have indicated the existence of a three dimensional region of the matrix in the vicinity of the fiber, which exhibits distinct properties. A key factor in the interphase formation of epoxy-diamine mixtures is the diffusivity of the diamine relative to the epoxy prepolymer. A technique for measuring diffusion coefficients of a liquid through solid polymeric thin layers is described. Infrared attenuated total reflectance (ATR) spectroscopy is used to analyze diffusion couples with infrared distinguishable bands. A cylindrical germanium crystal, coated with the polymeric layer of interest, is immersed in a boat cell filled with the diffusant, and infrared spectra of the system are taken in real time. By those means, only the region close to the solid surface is scanned without interferences from the bulk. The temperature dependence of diffusivity can also be evaluated by the use of a heated cell. Diffusivities that are evaluated in this way can be used to predict stoichiometric gradients during the curing reaction of the system and, therefore, the structure and property gradients of the material around the fiber. © 1994 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1994.070520909
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  • 6
    Electronic Resource
    Electronic Resource
    Characterization of coatings of poly(hexamethylene adipamide) deposited on carbon fibers by interfacial polymerization techniques (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 55 (1995), S. 1101-1110 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Polyamide coatings deposited on carbon fibers by means of an interfacial in situ polymerization technique have been examined. Two different coating processes were used, depending on the length of the carbon fibers (short or long). The effect of the concentration of the monomer reactants on the quantity of coating deposited on the fibers has been determined using thermogravimetric analysis (TGA). Characterization techniques used to identify the nature of the coating process product included Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). Using the above techniques, IR spectra were collected and identified, and important polymer properties, such as morphology, melting point, and the molecular weight of the polymer coating were determined. © 1995 John Wiley & Sons, Inc.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1995.070550713
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  • 7
    Electronic Resource
    Electronic Resource
    An experimental investigation of the effect of prepolymer molecular weight and stoichiometry on thermal and tensile properties of epoxy resins (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 62 (1996), S. 481-490 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An experimental study was undertaken to investigate the thermomechanical properties of a certain epoxy/amine configuration. The basic structure of all the epoxies was the same - DGEBA - and the curing agent used was PACM 20. By varying the epoxy prepolymer molecular weight and the stoichiometry between epoxy and amine, a range of different epoxy networks were produced. Glass transition temperatures were evaluated by using differentil scanning calorimetry (DSC). Modulus values as well as an alternative Tg determination were provided by dynamic mechanical analysis (DMA). Coefficients of thermal expansion were obtained from thermomechanical analysis (TMA). The tensile tests conducted at room and elevated temperatures provided additional modulus data along with the yield point, tensile strength, and elongation at break data. Property vs. stoichiometry curves exhibited a maximum for the glass transition temperature and the over the Tg modulus at the stoichiometric point. On the other hand, the under Tg modulus showed a minimum at the stoichiometric point. The results of the yield strength show remarkable similarity with the results of the modulus. Strength and elongation at break do not show clear trends, but a much different behavior is exhibited between room and elevated temperatures. © 1996 John Wiley & Sons, Inc.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of epoxy-amine stoichiometry on cured resin material properties (1992)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 46 (1992), S. 1863-1873 
    Details
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Sizings and/or surface treatments are commonly employed to enhance the interaction of fiber reinforcements in polymer matrix composites. These modifications can induce physical and chemical interactions that cause local stoichiometric imbalances to occur that can affect the properties of the polymer matrix in the vicinity of the fiber surface. This work reports the results of an experimental study of the influence of stoichiometric imbalance on the thermoelastic properties of an epoxy-amine resin. It is shown that the modulus and glass transition temperature are significantly affected by relatively small variations in stoichiometry. These results suggest that a fiber-induced interphase region in thermosetting composites can exhibit material properties that are significantly different from those of the bulk resin. © 1992 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/app.1992.070461018
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  • 9
    Electronic Resource
    Electronic Resource
    Analytic model for surface-induced molecular weight segregation in thermoplastic composites (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 2383-2394 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An analytic model based on a random-walk formulation for absorbing barriers is presented. The range of applicability of the model is established from results derived from Monte Carlo simulations. The model takes into account the influences of neutral, repulsive, and attractive polymer-surface interactions on the spatial variation of species concentrations in the vicinity of a surface. The model predicts that the lower molecular weight species of a polydisperse mixture will accumulate in the vicinity of a surface to create an interphase region. The extent of this surface-perturbed interphase region is on the order of three times the radius of gyration of the longest species of the mixture. The degree of molecular weight segregation is dependent upon the breadth of the molecular weight distribution. © 1994 John Wiley & Sons. Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1994.090321409
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  • 10
    Electronic Resource
    Electronic Resource
    A free-volume-based approach to modeling thermoset cure behavior (1990)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 28 (1990), S. 973-1000 
    Details
    ISSN: 0887-6266
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The free-volume theory for the temperature dependence of transport properties of glass-forming polymers is extended to obtain their relationship to the extent of cure. This treatment centers on the unifying role of molecular mobility and yields a model which connects extent of reaction, viscosity, diffusivity, ionic conductivity and dipole relaxation time. The temporal dependence of these properties is expressed by coupling the extended free-volume model with a relationship for the rate of cure, which included diffusional limitations. Analyses based on this model are applied to the observed behavior of a model epoxy-amine resin system. The intrinsic kinetics of this model system are shown to be first order. It is shown that diffusional limitations strongly affected the progress of the reaction in the final stages of cure. The diffusion-modified rate expression predictions agree with extent of reaction versus time data over the range of experimental temperatures. The temporal dependence of viscous behavior of the curing resin is measured. The extended free-volume model accurately describes the evolution of resin viscosity during cure. The dielectric behavior is similarly characterized and is in close agreement with the predictions of the general free-volume expression. The results of this study indicate that the free-volume theory modified to account for molecular weight effects allows prediction of resin properties with a two-parameter model. The results show that a power-law relationship exists between viscosity and ionic conductivity. This result suggests that electrical properties may be used for on-line measurement of resin viscosity during cure.
    Additional Material: 21 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1990.090280701
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