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Science 19 September 2003:
Vol. 301. no. 5640, pp. 1691 - 1695
DOI: 10.1126/science.1086952
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Research Articles

Neutron-Mapping Polymer Flow: Scattering, Flow Visualization, and Molecular Theory

J. Bent,1 L. R. Hutchings,1 R. W. Richards,1 T. Gough,2 R. Spares,2 P. D. Coates,2 I. Grillo,3 O. G. Harlen,4 D. J. Read,4 R. S. Graham,5 A. E. Likhtman,5 D. J. Groves,5 T. M. Nicholson,5,6 T. C. B. McLeish5*

Flows of complex fluids need to be understood at both macroscopic and molecular scales, because it is the macroscopic response that controls the fluid behavior, but the molecular scale that ultimately gives rise to rheological and solid-state properties. Here the flow field of an entangled polymer melt through an extended contraction, typical of many polymer processes, is imaged optically and by small-angle neutron scattering. The dual-probe technique samples both the macroscopic stress field in the flow and the microscopic configuration of the polymer molecules at selected points. The results are compared with a recent "tube model" molecular theory of entangled melt flow that is able to calculate both the stress and the single-chain structure factor from first principles. The combined action of the three fundamental entangled processes of reptation, contour length fluctuation, and convective constraint release is essential to account quantitatively for the rich rheological behavior. The multiscale approach unearths a new feature: Orientation at the length scale of the entire chain decays considerably more slowly than at the smaller entanglement length.

1 Department of Chemistry, Durham University, UK.
2 Department of Mechanical Engineering, Bradford University, UK.
3 Institut Laue Langevin, 38042 Grenoble, Cedex 9, France.
4 Department of Applied Mathematics, Leeds University, UK.
5 Department of Physics and Astronomy, Leeds University, UK.
6 Division of Chemical Engineering, University of Queensland, St. Lucia, Queensland 4072, Australia.

* To whom correspondence should be addressed. E-mail: t.c.b.mcleish{at}leeds.ac.uk

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Science. ISSN 0036-8075 (print), 1095-9203 (online)