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  • 2000-2004  (7)
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  • 1
    Electronic Resource
    Electronic Resource
    Simultaneous measurements of small angle x-ray scattering, wide angle x-ray scattering, and dielectric spectroscopy during crystallization of polymers (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 1733-1736 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A novel experimental setup is described which allows one to obtain detailed information on structural and dynamical changes in polymers during crystallization. This technique includes simultaneous measurements of small angle-wide angle x-ray scattering and dielectric spectroscopy (SWD). The capabilities of the technique have been probed by following in real time the crystallization process of a model crystallizable polymer: poly(ethylene terephthalate). By performing these experiments, simultaneous information from both, the amorphous and the crystalline phase is obtained providing a complete description of changes occurring during a crystallization process. The SWD technique opens up new promising perspectives for the experimental study of the relation between structure and dynamics in materials science. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150528
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Creep behavior and elastic properties of annealed cold-drawn poly(ethylene terephthalate): The role of the smectic structure as a precursor of crystallization (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 6006-6010 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The creep behavior and elastic properties of cold-drawn poly(ethylene terephthalate) (PET) films, annealed in the range 60–240 °C have been investigated by means of microindentation testing. Two indentation methods have been used. The imaging method has been employed to examine the viscoplastic properties of the polymer materials while the depth-sensing method was used for the determination of Young's modulus values. The creep behavior (plastic flow) of cold-drawn PET is shown to be intimately correlated to the nanostructural changes occurring upon annealing. The observed decrease in the rate of creep, when the glassy material is annealed at 60 °C, has been associated with the emerging smectic structure, which confers to the material a higher mechanical performance. The elastic properties of the smectic phase are found to be comparable to those of the glassy state. Young's modulus E values of the semicrystalline samples are discussed in light of the parallel model of crystalline and amorphous layers. E values are shown to depend on the crystalline lamellar thickness and the degree of crystallinity. Results suggest that Young's modulus values of the amorphous constrained regions within the crystals are higher than the E value of the fully amorphous material. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1418000
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Influence of cross-linking on the segmental dynamics in model polymer networks (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 447-452 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In an attempt to study the specific influence of cross-linking on the α relaxation in polymer networks, a series of model heterocyclic polymer networks (HPN) with well-defined cross-link densities and constant concentration of dipolar units were studied. Model HPN systems were prepared by simultaneous trimerization of 1,6-hexamethylene diisocyanate (HMDI) and hexyl isocyanate (HI). These HPN systems were characterized by dielectric relaxation spectroscopy in the 10−1 Hz〈F〈105 Hz frequency range and in the 123 K〈T〈493 K temperature interval. The α relaxation in these systems depends on network density and shifts toward higher temperatures as the cross-link density increases for high HMDI/HI ratios. Discussion of the α-relaxation shape in light of recent models indicates that segmental motions above the glass transition systematically experience a growing hindrance with increasing degree of cross-linking. Description of the temperature dependence of relaxation times according to the strong–fragile scheme clearly shows that fragility increases as polymer network develops. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481809
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  • 4
    Electronic Resource
    Electronic Resource
    The relationship between nonexponential relaxation and molecular stiffness in aromatic model compounds (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 5254-5256 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The α relaxation of a series of ether–ketone model compounds was studied to quantify the effect of molecular stiffness on the Kohlrausch–Williams–Watts stretching exponential. The obtained values decrease with increasing stiffness and are within the theoretical bounds predicted for systems with spatial dimensionality varying from 2 to 1. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481094
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  • 5
    Electronic Resource
    Electronic Resource
    Molecular dynamics and microstructure development during cold crystallization in poly(ether-ether-ketone) as revealed by real time dielectric and x-ray methods (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 115 (2001), S. 3804-3813 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The isothermal crystallization process of poly(ether-ether-ketone) from the glass has been studied in real time by dielectric spectroscopy and x-ray scattering experiments. The combination of these two techniques revealed a complete picture of the crystallization processes from the point of view of both amorphous and crystalline phases. Analysis of results shows that the sample morphology consists of lamellar stacks, separated by rather broad amorphous regions. The lamellar stacks are highly crystalline (∼70%), as obtained from both dielectric and x-ray scattering measurements, and the amorphous phase within the stacks is constrained up to a level where no segmental relaxation is possible. The remaining amorphous phase, after completion of the primary crystallization process, still has a certain mobility, but it is significantly slower than the initial amorphous mobility. Dielectric data and x-ray results are found to be highly congruent. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1388627
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  • 6
    Electronic Resource
    Electronic Resource
    Dielectric relaxation of heterocyclic polymer networks: Effect of the ratio and nature of the heterocyclic rings (2000)
    Springer
    Journal of materials science 35 (2000), S. 5021-5028 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Heterocyclic Polymer Networks (HPN) prepared by trimerization of 1,6-hexamethylene diisocyanate (HMDI) in presence of diglycidyl ether of bisphenol A (DGEBA) and triethylene diamine in two different regimes were characterized by dielectric spectroscopy in the 10−1–105 Hz frequency range and in the 123 K–423 K temperature interval. The dielectric experiments reveal the existence of multiple composition dependent relaxation processes. The γ process, appearing at low temperatures only in partially cured systems is related to the presence of free DGEBA. The β process is associated to local motions of the carbonyl groups present in the isocyanurate and oxazolidone cycles. The α relaxation, which has its origin in the segmental motions above the glass transition temperature, tends to appear at higher temperatures with increasing network junction density and with the degree of curing. The fragility and cooperativity of the α relaxation is discussed in terms of recent relaxation approaches.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004871413100
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  • 7
    Electronic Resource
    Electronic Resource
    Microhardness studies of chain-extended PE: II. Creep behaviour and temperature dependence (2000)
    Springer
    Journal of materials science 35 (2000), S. 1315-1319 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The variation of hardness with indentation time has been investigated for chain-extended polyethylene (PE), other PE samples crystallised under different conditions and paraffins. Hardness is shown to decrease with indentation time for all the samples investigated according to a power-law. Chain-extended PE, produced by high pressure crystallization or annealing, flows at the lowest rate under the indenter of all the PE samples considered. On the other hand, paraffins creep at the highest rate. Creep behaviour depends markedly on the crystal thickness of the material. The mechanical properties at long indentation times seem to be determined primarily by the deformation modes of the crystals. The temperature dependence of hardness and that of the creep behaviour has also been investigated. In chain-extended PE, the softening of the sample and the higher rate of creep with increasing temperature are discussed in terms of the thermal expansion of the unit cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004757402398
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