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  • 1
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An exact method is presented for calculating the density of states and any complex matrix element of the harmonic phonon Green's function of single polymer chains of infinite length. The method takes advantage of the one dimensionality of the Brillouin zone. In comparison to the standard root sampling method, the method presented here has all the advantages of a fully analytic procedure (in particular, smooth curves instead of histograms) and offers and enormous increase in accuracy while at the same time drastically decreasing the computer time. For illustrational purposes, the method is applied to the defect model of Opaskar and Krimm and to the diatomic linear chain. In addition to the reproduction of the results obtained by Opaskar and Krimm, explicit expressions for the resonance and localized modes are derived.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A theoretical description of the ductile transition of glassy polymers in tensile creep is given. It predicts the delay time for plastic yield as a function of stress. The model assumes first-order rate expressions for the rate of change of loadbearing elements. The rate constants are given by a modification of the absolute reaction rate concepts of Eyring, where the energy barrier for breakdown of the bonding elements is asymmetric. This leads to an equation for the yield delay time as a function of the height of the energy barrier in the unstressed state, an activation volume, and a critical stress required to overcome the initial barrier asymmetry. The model has been compared to creep delay time experiments on polysulfone, polycarbonate, and poly(methyl methacrylate). It is able to predict the stress dependence for the onset of ductility in these materials with greater accuracy than previously reported equations.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A closed-form solution for the stress distribution in a cylindrical elastic rod under finite torsion is given involving use of the logarithmic λ form of the strain-energy function proposed by Valanis and Landel. Experimental torque data on natural rubber which give support to the present solution over a large range of angles of twist are shown. It is also shown how torsion data may be used to determine the λ form for deformations that lie outside the range of applicability of the logarithmic function if certain conditions apply. A solution, also in closed form, is given by using another λ form proposed by Dickie and Smith on the basis of experiments on styrene - butadiene rubber.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The orientation of crystallites in a bundle of parallel cotton fibers was studied by x-ray diffraction. The intensity distributions of the 101 and 002 diffraction rings showed the distributions of (101) and (002) planes to be identical within the limits of accuracy. Therefore, the crystallites in the cotton fibers very likely had random orientation about their long axes. The orientation distribution of these axes was calculated by using the intensity distribution of the 002 diffraction ring. The cylindrically symmetrical density distribution J(β) thus obtained was multiplied by sin β to obtain the distribution of relative numbers of crystallites at given angles β to the long axis of the fiber. The average 〈β〉 was found to be in agreement with the value of 〈sin2β〉 measured from the 002 diffraction ring. The intensity distributions on the 101 and 002 diffraction rings showed small fluctuations. These fluctuations appeared much stronger in the J(β) and sin β J(β) distributions, indicating clear discontinuities in the pitch angle distribution.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Examination of longitudinal, cross, and skew sections of extruded polycaprolactam filaments with the polarizing light microscope reveal morphological features not previously described. In cross-sectional view, three distinct layers enclose a “homogeneous” central matrix. The outermost layer is characterized by large, birefringent, truncated cones extending upward from the surface. Associated with the cones and an entity in its own right is what appears to be a second layer of ultrafibrils. Below the latter is a fine-structured layer of submicroscopic spherulites. A combination of the above features forms the transcrystalline region of stressed melts. Row nucleation is evident on the surface of the filaments.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Transmission electron microscopy and electron diffraction were used to study the molecular structure of fibers drawn from polyethylene single crystals at 77, 293, and 383°K. The results suggest that the formation of the fibers occurs by a two-step process. The first step is the breaking off of single blocks of folded chains from the single crystals so that a “string-of-pearls” structure is obtained. If the temperature is sufficiently high this process is followed by the thermally activated rearrangement of the molecules in the drawn fibers so that a “bamboo” structure results.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A description is given of an apparatus for the continuous recording during crystallization of the spherulite radius, in the range of one half micron to a few microns, by scanning the Hv scattering pattern. At the same time the apparatus measures the change in intensity of the transmitted depolarized light, which is a measure of the overall rate of crystallization. The theoretical aspects of this measuring procedure are briefly discussed on the basis of light scattering by perfect and imperfect spherulites.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Based on an analogy with the growth of kink bands in oriented and annealed crystalline polymers, a mechanism is suggested for the deformation-induced spherulite-to-fibril transformation. Oriented and annealed material was employed as a model because it has roughly the same structure as the lamellar bundle of the spherulite. Under conditions that minimize the fibrillar quality and maximize the lamellar bundle quality, oriented and annealed crystalline polymers deform with the formation and growth of kink bands. The characteristics of kink bands are the sharpness of the kinks, occurring within zones ca. 100 Å wide, and mirror symmetry of the fibrils about the kink-zone planes. The spherulite-fibril transformation is suggested by analogy, then, to occur in the narrow zones that indeed are often found and to result in mirror symmetry of the chain axes about the transformation-zone planes, which may not exactly occur because of a tendency for the tie molecules to be pulled from the lamellae during drawing. The implications for the transformation are (a) that the microfibril backbones are derived from the tie molecules between lamellae and (b) though some unfolding occurs as blocks that were adjacent within the lamellae become separated, the crystals remain mostly intact during the transformation. The analog is supported by or at least is consistent with various other results, including those from morphological and small- and wide-angle x-ray studies.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We examine several methods for analyzing the spectrum of light scattered from polydisperse polymer solutions. General expressions are reviewed for the inelastic scattering spectra and integrated intensities due to the pure translational normal mode of motion, using both heterodyne and homodyne detection, in terms of the molecular weights, concentrations, scattering form factors, and diffusion coefficients of the individual polymeric species, These results are used to obtain general expressions for the limiting slopes and intercepts of various rearranged versions of the equation I(v) = (A/π)2/(v2 + γ2) that permit linear plotting: I(v) is the intensity of light scattered at frequency v, A is the integrated intensity, and γ is the spectral halfwidth, K2D/2π, where K is the scattering vector and D the diffusion coefficient. These results are applied to the special case of a Schulz-Zimm distribution, neglecting form factors, to obtain explicit expressions relating the average diffusion coefficients determined by these procedures to other measurable quantities: the mean polymer radius; the diffusion coefficient of the weight-average species; and, together with the weight-average sedimentation coefficient, the weight-average molecular weight. Numerical calculations for two particular cases indicate the relative merits of the various data analysis procedures. Homodyne detection gives average values that are closer to weight averages than does heterodyne detection.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
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