Entangled rigid macromolecules under continuous startup shear deformation: Consequences of a microscopically anharmonic confining tube

Daniel M. Sussman, Kenneth S Schweizer

Research output: Contribution to journalArticlepeer-review

Abstract

We build upon our recently developed microscopic theory for the tube confinement potential of rigid macromolecules to treat the relaxation of stress and orientation of fluids of topologically entangled needles during a continuous startup shear deformation. Two coupled and highly nonlinear evolution equations for stress and rod orientation are proposed. The novel feature is our ability to self-consistently relate the current stress- and orientation-dependent state of the fluid with an effective instantaneous relaxation time that combines (perturbed) reptation and transverse activated barrier hopping. The effective relaxation time follows from a microscopic, time-dependent prediction of the tube confinement potential during the deformation. Results for the strain and Weissenberg number dependence of the confinement potential are presented for two degrees of entanglement. As a natural consequence of the predicted stress dependence of the confinement potential, our self-consistent single-rod theory emergently manifests features normally associated with many-polymer convective constraint release, such as a monotonic flow curve and an effective relaxation time that (nearly) scales with the inverse of the deformation rate. Comparisons with the original Doi-Edwards theory reveal qualitative differences as a consequence of stress- and orientation-induced softening of the tube constraints. Severe tube dilation often occurs, and the complete destruction of transverse localization is possible depending on system-specific conditions.

Original languageEnglish (US)
Pages (from-to)5684-5693
Number of pages10
JournalMacromolecules
Volume46
Issue number14
DOIs
StatePublished - Jul 23 2013

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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