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  • 1
    Electronic Resource
    Electronic Resource
    Memory and switching effects in polycarbonate-graphite composites (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 1061-1063 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Reproducible memory and switching effects have been detected in polycarbonate-graphite composites. Memory effects are characterized in the range of 0–1 kV/cm. It is suggested that they involve electrothermal and electromechanical phenomena. Switching effects occur above 2 kV/cm and are related to an intrinsic electric breakdown of the material. The threshold field increases with increasing thickness of the composite film. The temperature dependence and level of conductivity reached point toward a prevailing electron tunneling mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336217
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  • 2
    Electronic Resource
    Electronic Resource
    Structural implications on positron lifetimes in lamellar polyethylene with chain defects (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 253-259 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: New positron lifetime data in a series of isothermally crystallized polyethylene pairs with known concentrations of chain defects, having a lamellar structure, have been measured. The materials were characterized by small-angle and wide-angle x-ray scattering techniques. Positron lifetime data were computer analyzed and only three components could be resolved. It is shown that the annihilation mechanisms can be understood in terms of average distance between lamellar crystals (long period), crystal thickness, and chain defect concentration. The present results confirm, in consonance with the conclusions of other authors, the longest component to be due to ortho-positronium pick-off annihilation. The intermediate component may be ascribed to positronium trapped at the crystal-amorphous interface. The application of a three-state trapping model yields a lifetime of about 900 ps for this state. It is suggested that the shortest component may be due to free positron annihilation, para-positronium self-annihilation, and annihilation of positrons from a tightly bound state localized at the chain defects. An approximate calculation provides lifetime values around 250 ps for this short-lived state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.335720
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    X-ray diffraction study of poly-p-phenylene doped with SbF5 and SbCl5 (1989)
    Springer
    Polymer bulletin 21 (1989), S. 635-639 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract X-ray diffraction experiments have been performed on SbF5 and SbCl5 doped PPP prepared by the Kovacic method. Results are discussed in terms of two structural models which account for the regular intercalation of dopants within the polymer crystal lattice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00264146
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  • 4
    Electronic Resource
    Electronic Resource
    Hardness of nitric acid treated polyethylene followed by recrystallization (1987)
    Springer
    Colloid & polymer science 265 (1987), S. 37-41 
    Details
    ISSN: 1435-1536
    Keywords: Microhardness ; polyethylene ; fuming nitric acid ; dicarboxylic acids
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The hardness variation of melt crystallized polyethylene as a consequence of controlled fuming nitric exposure has been investigated using the microindentation technique. This study complements previous results obtained using other reagents (H2SO4, ClHSO3). After HNO3 exposure the microhardness of polyethylene decreases very rapidly, instead of increasing after the first hours of treatment. The hardness decrease is correlated to the volume fraction of interlamellar microvoids arising through selective acid digestion. For longer treatment times (t〉40 h) the fragility of the material increases and the sample collapses under the indenter. The hardening of the degraded material after recrystallization from the melt is followed as a function of treatment time. The results are discussed in the light of the molecular mechanisms involved. Comparison of the experimental data with hardness calculations for ideal PE lamellar structures and chain extended dicarboxylic crystals implies that the major contribution to hardening is due to electron dense groups attachment at the surface of a mixed lamellar structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01422661
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  • 5
    Electronic Resource
    Electronic Resource
    Equilibrium and non-equilibrium melting of branched polyethylene relating to defect incorporation within crystals (1987)
    Springer
    Colloid & polymer science 265 (1987), S. 239-245 
    Details
    ISSN: 1435-1536
    Keywords: Branchedpolyethylene ; equilibriummelting point ; enthalpy offusion ; surface free energy ; kinks ; chain defects
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract New equilibrium melting point data, for polyethylene containing chain defects, are tested in the light of random copolymer predictions. A simplified expression for the melting point depression of random copolymers containing small amounts of non-crystallizable units is derived. Non-equilibrium melting data for rapidly quenched polyethylene samples are also reported. The fusion enthalpyΔH∘(X), and the surface free energyσ e for crystals containing defects are evaluated using crystallinity, equilibrium meltingtemperatures and X-ray long period data. It is shown that increasing defect penetration within crystals induces a decrease ofΔH∘(X) withX in accordance with theoretical predictions. Finallyσ e is, similarly, shown to decrease with increasing number of chain defects attached to the crystal surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01412713
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  • 6
    Electronic Resource
    Electronic Resource
    New aspects of yielding in semicrystalline polymers related to microstructure: Branched polyethylene (1988)
    Springer
    Colloid & polymer science 266 (1988), S. 29-34 
    Details
    ISSN: 1435-1536
    Keywords: Semicrystalline polymers ; hardness ; yielding ; micro-structure ; crystal size
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The application of thermodynamics of eutectoid copolymers and a generalized Tabor-relation to relationships between mechanical properties (microhardness, yield stress) and microstructure in semicrystalline polymers is considered. The approach is illustrated by results on melt-crystallized low density polyethylene, investigated near the yield point at different temperatures. The success of the approach emphasizes that semicrystalline polymers, despite being viscoelastic hetereogeneous systems, give rise to a yielding process entailing the irreversible deformation of a larger number of crystals within cooperative super-structure units. Microhardness provides, within this context, a unique measure of the crystal size average. Comparison of calculated and experimental data favors the view of deformed crystals containing basal defective surface boundaries (“meso-crystals”) which yield cooperatively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01451528
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  • 7
    Electronic Resource
    Electronic Resource
    Changes in defect concentration within polymer crystals: annealing of isotropic and drawn polyethylene (1986)
    Springer
    Colloid & polymer science 264 (1986), S. 123-127 
    Details
    ISSN: 1435-1536
    Keywords: Polyethylene ; chain defects ; lattice constants ; annealing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An estimation of the changes in the level of chain defects (branches) accommodated within crystals of undrawn and drawn branched polyethylene, subsequently annealed, is carried out in the light of unit cell expansion data. The results reveal that annealing affects the estimated crystalline defect concentration differently depending on whether the material was drawn or undrawn. Thus, annealing of drawn polyethylene with a defect concentration of 3 % results in a healing of crystal defects, due to a preferential rejection of branches from the crystals. In contrast, annealing of melt crystallized branched polyethylene does not influence the average concentration of chain defects within the crystal despite the increase in lamellar thickness. The branches are trapped into the much wider lamellar crystals with fewer grain boundaries available and defect sequences cannot diffuse out of the crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01414837
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  • 8
    Electronic Resource
    Electronic Resource
    Percolation threshold of conductive polycarbonate/carbon composites as revealed by electron microscopy (1986)
    Springer
    Journal of materials science 5 (1986), S. 1065-1066 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01730285
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  • 9
    Electronic Resource
    Electronic Resource
    Recent developments in the understanding of the microhardness of paraffins (1986)
    Springer
    Journal of materials science 5 (1986), S. 1183-1185 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01742241
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  • 10
    Electronic Resource
    Electronic Resource
    Phase changes in isotactic polypropylene measured by microhardness (1988)
    Springer
    Journal of materials science 7 (1988), S. 165-166 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01730607
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