Relating Chain Conformations to Extensional Stress In Entangled Polymer Melts

Abstract

Nonlinear extensional flows are common in polymer processing but remain challenging theoretically because dramatic stretching of chains deforms the entanglement network far from equilibrium. Here, we present coarse-grained simulations of extensional flows in entangled polymer melts for Rouse-Weissenberg numbers $W{i}_R=0.06$-$52$ and Hencky strains $\epsilon \ge 6$. Simulations reproduce experimental trends in extensional viscosity with time, rate and molecular weight. Studies of molecular structure reveal an elongation and thinning of the confining tube with increasing $W{i}_R$. The rising stress is quantitatively consistent with the decreasing entropy of chains at the equilibrium entanglement length. Molecular weight dependent trends in viscosity are related to a crossover from the Newtonian limit to a high rate limit that scales differently with chain length.

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• Multiscale equilibration of highly entangled isotropic model polymer melts
• Molecular mechanisms of self-mated hydrogel friction
• Shear Is Not Always Simple: Rate-Dependent Effects of Flow Type on Granular Rheology
• Topological transition in multicyclic chains with structural symmetry inducing stress-overshoot phenomena in multicyclic/linear blends under biaxial elongational flow
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• Comment on: "Relating Chain Conformations to Extensional Stress in Entangled Polymer Melts"
• O'Connor, Alvarez, and Robbins Reply to Xu et al. (arXiv:1808.05390)
• Identifying the Threshold Chain Length for Stress Overshoot in Ring-Linear Polymer Blends under Uniaxial Elongation: The Role of Multiple Threading
• Convergence of Nonequilibrium Langevin Dynamics for Planar Flows