We report upon the characterization of the steady-state shear stresses and first normal stress differences as a function of shear rate using mechanical rheometry (both with a standard cone and plate and with a cone partitioned plate) and optical rheometry (with a flow-birefringence setup) of an entangled solution of asymmetric exact combs. The combs are polybutadienes (1,4-addition) consisting of an H-skeleton with an additional off-center branch on the backbone. We chose to investigate a solution in order to obtain reliable nonlinear shear data in overlapping dynamic regions with the two different techniques. The transient measurements obtained by cone partitioned plate indicated the appearance of overshoots in both the shear stress and the first normal stress difference during start-up shear flow. Interestingly, the overshoots in the start-up normal stress difference started to occur only at rates above the inverse stretch time of the backbone, when the stretch time of the backbone was estimated in analogy with linear chains including the effects of dynamic dilution of the branches but neglecting the effects of branch point friction, in excellent agreement with the situation for linear polymers. Flow-birefringence measurements were performed in a Couette geometry, and the extracted steady-state shear and first normal stress differences were found to agree well with the mechanical data, but were limited to relatively low rates below the inverse stretch time of the backbone. Finally, the steady-state properties were found to be in good agreement with model predictions based on a nonlinear multimode tube model developed for linear polymers when the branches are treated as solvent.
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Research Article|
May 01 2016
Viscoelasticity and nonlinear simple shear flow behavior of an entangled asymmetric exact comb polymer solution
F. Snijkers;
F. Snijkers
a)
Foundation for Research and Technology Hellas (FORTH),
Institute of Electronic Structure and Laser
, Heraklion, Crete 70013, Greece and CNRS/Solvay UMR 5268, Laboratoire Polymères et Matériaux Avancés, Saint-Fons 69192, France
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K. M. Kirkwood;
K. M. Kirkwood
Department of Chemical Engineering,
University of California Santa Barbara
, Santa Barbara, California 93106
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D. Vlassopoulos;
D. Vlassopoulos
Foundation for Research and Technology Hellas (FORTH),
Institute of Electronic Structure and Laser
, Heraklion, Crete 70013, Greece
and Department of Materials Science and Technology, University of Crete
, Heraklion 71003, Crete, Greece
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L. G. Leal;
L. G. Leal
Department of Chemical Engineering,
University of California Santa Barbara
, Santa Barbara, California 93106
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A. Nikopoulou;
A. Nikopoulou
Department of Chemistry,
University of Athens
, Athens 15784, Greece
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N. Hadjichristidis;
N. Hadjichristidis
KAUST Catalysis Center, Polymer Synthesis Laboratory, Division of Physical Sciences and Engineering,
King Abdullah University of Science and Technology (KAUST)
, Thuwal 23955-6900, Kingdom of Saudi Arabia
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S. Coppola
S. Coppola
Centro Ricerche Elastomeri
, Versalis S.p.A., Ravenna, Italy
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a)
Author to whom correspondence should be addressed; electronic mail: [email protected]
J. Rheol. 60, 451–463 (2016)
Article history
Received:
December 14 2015
Accepted:
March 02 2016
Citation
F. Snijkers, K. M. Kirkwood, D. Vlassopoulos, L. G. Leal, A. Nikopoulou, N. Hadjichristidis, S. Coppola; Viscoelasticity and nonlinear simple shear flow behavior of an entangled asymmetric exact comb polymer solution. J. Rheol. 1 May 2016; 60 (3): 451–463. https://doi.org/10.1122/1.4944993
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