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  • 1
    Electronic Resource
    Electronic Resource
    Extensional viscosity from entrance pressure drop measurements (1997)
    Springer
    Rheologica acta 36 (1997), S. 144-151 
    Details
    ISSN: 1435-1528
    Keywords: Extensional viscosity ; entrance pressure drop method ; Cogswell's analysis ; extensional strain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Extensional rheological properties are important in characterization and processing of polymeric liquids. The use of entrance pressure drop to obtain extensional viscosity is particularly attractive because it can be applied to both low and high viscosity liquids using the Bagley correction obtained from a conventional capillary rheometer. Low density polyethylene of three different melt index values, including IUPAC-X (a different batch of IUPAC-A), and a high density polyethylene were tested using a commercial capillary rheometer. The entrance pressure drop (ΛP en ) was obtained with a “zero-length” orifice die with an abrupt contraction. The contraction ratio was 12:1. Predictions from several approximate analyses to calculate the uniaxial extensional viscosity ηu (using an axisymmetric contraction) from ΔP en were compared. These comparisons are summarized in the appendices. Due to the transient nature of contraction flows, η u is also a function of the strain (ɛ). This was examined by comparing η u from ΔP en (Cogswell's analysis was chosen for convenience) with transient extensional viscosity (η u +) at different magnitudes of ɛ from fiber-windup technique (Padmanabhan et al., 1996). η u + at ɛ≈ 3 was found to be close to η u from ΔP en (using Cogswell's analysis) for two LDPE samples that had fiber-windup data available. The magnitude of the strain in the contraction did not vary with strain rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00366820
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  • 2
    Electronic Resource
    Electronic Resource
    Can extensional viscosity be measured with opposed-nozzle devices? (1997)
    Springer
    Rheologica acta 36 (1997), S. 429-448 
    Details
    ISSN: 1435-1528
    Keywords: Extensional viscosity ; extensional flow ; elongational viscosity ; opposed nozzles ; extensional rheometry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Opposed-nozzle devices are widely used to try to measure the extensional viscosity of low-viscosity liquids. A thorough literature survey shows that there are still several unanswered questions on the relationship between the quantity measured in opposed-nozzle devices and the “true” extensional viscosity of the liquids. In addition to extensional stresses, opposed nozzle measurements are influenced by dynamic pressure, shear on the nozzles, and liquid inertia. Therefore the ratio of the apparent extensional viscosity that is measured to the shear viscosity that is independently measured is greater than three even for Newtonian liquids. The effect of inertia on the extensional measurements is analyzed by computer-aided solution of the Navier-Stokes system, and by experiments on low-viscosity Newtonian liquids (1 mPa s〈/ηS ⩽ 800 mPa s). The effect of nozzle separation-to-diameter ratio on the average residence time of the liquid is analyzed under the assumption of simple extensional flow kinematics. The average residence time of the liquid is independent of this ratio unless the radial inflow section of the extensional flow volume is related to the nozzle separation. Experiments indicate that in some cases widening the gap lowers the apparent extensional viscosity that is measured, whereas in other cases the opposite is true. In the light of these theoretical considerations and experimental observations, the use of systematic corrections to extensional viscosity measurements on non-Newtonian liquids is not recommended. Thus opposed nozzle devices should be considered as useful indexers rather than rheometers. Finally, measurements on a series of semi-dilute solutions of high molecular weight poly(ethylene oxide) in. water are also reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396329
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  • 3
    Electronic Resource
    Electronic Resource
    Microstructure of triblock copolymers in asphalt oligomers (1997)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 2857-2877 
    Details
    ISSN: 0887-6266
    Keywords: block copolymer ; asphalt ; microstructure ; oligomer ; SEBS ; TEM ; SAXS ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: A model asphalt has been separated into two parts, asphaltene and maltene, through solvent extraction by n-heptane. The interactions of asphaltene and maltene with the triblock copolymer poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) were investigated by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), dynamic mechanical analysis (DMA), and differential scanning calorimetry (DSC). Asphaltene was found to be essentially immiscible with both blocks of SEBS, while maltene was miscible with SEBS. An unusual sequence of morphological transformations of SEBS microstructure with respect to the addition of maltene was observed. The morphology transformed from hexagonal cylinder, to perforated layers, to lamellae and then back to the original hexagonal cylinder. The observed transformation reflects a limited solubility for both S and EB domains: at lower concentration maltene is a preferential additive for S domains, while increasing concentration the swelling of EB-rich microdomains by maltene becomes significant. The basic understanding of the interactions of the components of asphalt with SEBS gives a simple path to characterize and predict the microstructure of triblock copolymers in asphalt oligomers. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2857-2877, 1997
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
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