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  • 1
    Electronic Resource
    Electronic Resource
    The “decaying springs” model for irreversibility in polymer melts (1997)
    Springer
    Rheologica acta 36 (1997), S. 585-589 
    Details
    ISSN: 1435-1528
    Keywords: Polymer melts ; viscoelasticity ; constitutive equations ; irreversibility ; integral models ; thermorheological behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract In this work, entanglements in a polymer melt are modeled as a system of parallel springs which form and decay spontaneously. The springs are assumed to be nonlinear, and a certain fraction of them is torn apart by a certain strain. Based on these assumptions, a model of behavior in simple shear is developed. This model is shown to predict a behavior comprising that of a Wagner fluid, and is generalized to a tensorial model of single integral type. The integrand depends on a product of a material function, modeling reversible behavior, and a material functional which takes irreversible processes into account. Irreversibility of network disentanglement, which may occur when deformation changes or reverses direction, can be modeled in this way. It is shown that the two well-known Wagner constitutive equations with and without irreversibility assumptions are special cases of the model developed. In case of a deformation which does not change directions, the new material function and the material functional are multiplied to yield Wagner's damping function. When the rate of spring formation is a function of temperature, the developed model is shown to predict thermorheologically simple behavior. A constitutive equation for non-isothermal flow of polymers is developed with this assumption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00368136
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    The „decaying springs” model for irreversibility in polymer melts (1997)
    Springer
    Rheologica acta 36 (1997), S. 585-589 
    Details
    ISSN: 1435-1528
    Keywords: Key words Polymer melts ; viscoelasticity ; constitutive equations ; irreversibility ; integral models ; thermorheological behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract In this work, entanglements in a polymer melt are modeled as a system of parallel springs which form and decay spontaneously. The springs are assumed to be nonlinear, and a certain fraction of them is torn apart by a certain strain. Based on these assumptions, a model of behavior in simple shear is developed. This model is shown to predict a behavior comprising that of a Wagner fluid, and is generalized to a tensorial model of single integral type. The integrand depends on a product of a material function, modeling reversible behavior, and a material functional which takes irreversible processes into account. Irreversibility of network disentanglement, which may occur when deformation changes or reverses direction, can be modeled in this way. It is shown that the two well-known Wagner constitutive equations with and without irreversibility assumptions are special cases of the model developed. In case of a deformation which does not change directions, the new material function and the material functional are multiplied to yield Wagner’s damping function. When the rate of spring formation is a function of temperature, the developed model is shown to predict thermorheologically simple behavior. A constitutive equation for non-isothermal flow of polymers is developed with this assumption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003970050073
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Birefringence measurements in extensional flow of polyisobutylene around an expanding bubble (1998)
    Springer
    Rheologica acta 37 (1998), S. 182-188 
    Details
    ISSN: 1435-1528
    Keywords: Key words Polymer melts ; viscoelasticity ; birefringence ; elongational flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Birefringence in liquid polymers offers the possibility of obtaining information about stress in complex flows. In this work, this is done for extensional flows of polyisobutylene in a “breathing bubble” rheometer. In this type of rheometer, a bubble consisting of an incompressible, low-viscosity fluid (usually water) is injected into the sample with a nozzle. Expanding or collapsing the bubble by adding or removing water induces biaxial or uniaxial extension in the surrounding sample. The pressure difference between the bubble and the surroundings can be measured and compared to the predictions of constitutive equations. This measurement only gives one integral value for a complex flow history. In this paper, the birefringence around the bubble is measured in order to learn more about the flow. This is done by comparing pressure and birefringence results to those of standard constitutive equations for a polyisobutylene sample. A good agreement between the pressure and optical measurements and the theory is found with a single value of the stress-optical constant.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003970050104
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    Paper (German National Licenses)
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