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  • 1
    Electronic Resource
    Electronic Resource
    The relaxation of linear flexible polymers which are slightly poly-disperse (1996)
    Springer
    Rheologica acta 35 (1996), S. 645-655 
    Details
    ISSN: 1435-1528
    Keywords: Rheology ; polymers ; poly-dispersity ; linear viscoelasticity ; relaxation time
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The relaxation of slightly poly-disperse linear flexible polymers has been expressed in a simplified blending rule which is presumed to be a weighted linear superposition of the relaxation spectra of mono-disperse components which constitute the blend. Discrete components are characterized by their molecular weight M i,weight fraction w i,and relaxation time spectrum H i(λ). ). In contrast to broadly distributed blends in which the small molecules mobilize the large ones and vice versa, we introduce the term “slightly polydisperse” for blends with molecular weight distributions narrow enough to have very little change in the longest relaxation times of each molecular weight component. The properties of this blending rule are analyzed and dynamic data is calculated for slightly poly-disperse polystyrene. As an application, the blending rule is used to determine the characteristic mono-disperse parameters (BSW parameters) of two materials, poly (vinyl methyl ether) and polycarbonate, for which we could not determine their BSW parameters directly since they were not available in nearly monodisperse form. The proposed blending rule can only be applied to systems in which all components are above the entanglement molecular weight, i.e. M i≫M c.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396513
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  • 2
    Electronic Resource
    Electronic Resource
    Rotation of liquid crystalline macromolecules in shear flow and shear-induced periodic orientation patterns (1996)
    Springer
    Rheologica acta 35 (1996), S. 160-167 
    Details
    ISSN: 1435-1528
    Keywords: Rheology ; liquid crystal ; monodomain ; instability ; conoscopy ; shear
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract We have measured the shear-induced rotation of the nematic director in a liquid crystalline polymer using poly benzyl glutamate (PBG) as model system. PBG is a well characterized synthetic poly (α amino acid) with rigid chain architecture and well defined conformations. For the experiments it is important to start out with a sample in which the molecules are highly aligned with a uniform director. This so-called monodomain morphology is obtained by use of strong magnetic fields and surface modifications of the sample holders. When shearing the monodomain at a constant rate, the macromolecules rotate initially homogeneously until a periodic director pattern develops. These spatially periodic structures emerge in a narrow range of shear strain and, as shearing continues, disintegrate into a chaotic texture. By varying the initial monodomain director with respect to the flow direction (but within the shear planes) we could show that the periodic patterns do not depend on the shear direction; they are governed by the director of the initial monodomain. We observe conoscopically that at high shear rates the texture becomes uniformly aligned. The molecules are aligned preferentially with an angle of about 4° to the shear direction (against vorticity direction). Interestingly, this agrees very well with predictions made by Larson (1990).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396043
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