No Access Submitted: 25 October 2006 Published Online: 01 March 2007
Journal of Rheology 51, 275 (2007); https://doi.org/10.1122/1.2433701
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  • a)Author to whom correspondence should be addressed; electronic mail: [email protected]

    b)Currently at Bridgestone Americas Center for Research and Technology.

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  • Y. Thomas Hu
  • Larry Wilen
  • Amy Philips
  • Alex Lips
The dynamic and steady state behavior of highly entangled polybutadiene solutions has been studied in shearing flow using high-spatial-resolution particle tracking velocimetry. In Couette geometry, the velocity profile is approximately linear upon the imposition of a step shear rate, but becomes significantly curved at later times, and attains the steady shape only after more than 100 strain units. In steady state, local shear rate varies smoothly across the gap and there is no shear banding. The constitutive relation is constructed from local stress and local shear rate extracted from velocity profiles. This procedure is not affected by the common problems of slip and edge instabilities as encountered with cone and plate geometry. The constructed constitutive curve is clearly monotonic for all tested solutions with entanglement numbers up to 47, notwithstanding a local power law index in the stress plateau as small as 0.01. The slope of the stress plateau is sensitive to both the chain polydispersity and entanglement number. Transient shear banding was observed under imposition of step shear in cone and plate geometry. This banding, however, disappears at longer times, which again confirms a monotonic steady state constitutive relation.
We would like to thank Jim Oberhauser and Tom McLeish for discussions.
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