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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Rheologica acta 34 (1995), S. 317-320 
    ISSN: 1435-1528
    Keywords: Free damped oscillations ; linear viscoelasticity ; forced oscillations ; dynamic rheometric functions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract This work shows that the complex dynamic viscosity η* (ω) can be evaluated from experimental data of free damped oscillations (FDO) when upper and lower angular displacements measured in a plate-plate geometry are analyzed by Fourier series. We deduce the equation required to evaluate experimentally the dynamic functions of linear viscoelastic materials in FDO. Two loss tangents can be defined in FDO, which are not necessarily equal to tan δ(ω) of the forced oscillation test.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Rheologica acta 37 (1998), S. 449-462 
    ISSN: 1435-1528
    Keywords: Key words Linear polydimethylsiloxanes ; molecular weight distribution ; polymer relaxation mechanisms ; chain reptation with contour length fluctuations ; tube constraint release
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Although it is known that chain reptation with contour length fluctuations and tube constraint release are the relevant mechanisms of chain relaxation, only applications of the theory to specific polymers could allow one to determine the relative importance of these relaxation modes. With this purpose we study the relation between the shear relaxation modulus of entangled, linear and flexible polydimethylsiloxane (PDMS) samples with narrow molecular weight distribution (MWD) and some of their blends. The linear PDMS are synthesized by anionic polymerization. Binary blends having different concentrations of the linear PDMS with narrow MWD are also prepared.  A theory developed by some of the authors has been proposed previously and is based on the double reptation mixing rule and a law for the relaxation time of the chains. Since, calculations in the theory must be carried out with rheometric data of linear viscoelasticity, the time-temperature superposition principle is used at a reference temperature of 20°C to obtain the and master curves. We conclude that the PDMS chains in a matrix with 1.5 relax predominantly by reptation while the tube renewal follows Rouse mode, which is proportional to chain molecular weight raised to the square power. It is also shown that dilution effects due to short chains start to be important in the binary blends of PDMS samples due to the presence of Zimm mode of relaxation, which is suggested by the theory for linear polymers of relatively high polydispersity.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 56 (1995), S. 967-977 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This work studies the evolution of dynamic rheometric functions (dynamic viscosity η′(ω) and storage modulus G′(ω)) with the degree of vulcanization and temperature of well-characterized SBR and NBR compounds. Experiments are carried out in an oscillating bicone cell, and results are well fitted through a model that considers flow kinematics, heat transfer, curing kinetics, and rheological functions. It is possible to quantify the model parameters and to understand better the evolution of filled rubber compounds toward crosslinked networks or vulcanizates. Conclusions are also obtained on the interplay between rheological functions and molecular parameters (average molecular weight and polydispersity). Experimental evaluations of the ratios between oscillating torques, at different times of the curing process, correlate directly with changes in rheological properties of the samples studied. © 1995 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Publication Date: 1999-02-10
    Print ISSN: 0021-8561
    Electronic ISSN: 1520-5118
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
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