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Issue 14, 2016
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Finite cohesion due to chain entanglement in polymer melts

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Three different types of experiments, quiescent stress relaxation, delayed rate-switching during stress relaxation, and elastic recovery after step strain, are carried out in this work to elucidate the existence of a finite cohesion barrier against free chain retraction in entangled polymers. Our experiments show that there is little hastened stress relaxation from step-wise shear up to γ = 0.7 and step-wise extension up to the stretching ratio λ = 1.5 at any time before or after the Rouse time. In contrast, a noticeable stress drop stemming from the built-in barrier-free chain retraction is predicted using the GLaMM model. In other words, the experiment reveals a threshold magnitude of step-wise deformation below which the stress relaxation follows identical dynamics whereas the GLaMM or Doi–Edwards model indicates a monotonic acceleration of the stress relaxation dynamics as a function of the magnitude of the step-wise deformation. Furthermore, a sudden application of startup extension during different stages of stress relaxation after a step-wise extension, i.e. the delayed rate-switching experiment, shows that the geometric condensation of entanglement strands in the cross-sectional area survives beyond the reptation time τd that is over 100 times the Rouse time τR. Our results point to the existence of a cohesion barrier that can prevent free chain retraction upon moderate deformation in well-entangled polymer melts.

Graphical abstract: Finite cohesion due to chain entanglement in polymer melts

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Article information

19 Jan 2016
19 Feb 2016
First published
22 Feb 2016

Soft Matter, 2016,12, 3340-3351
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Finite cohesion due to chain entanglement in polymer melts

S. Cheng, Y. Lu, G. Liu and S. Wang, Soft Matter, 2016, 12, 3340
DOI: 10.1039/C6SM00142D

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