Relating Chain Conformations to Extensional Stress in Entangled Polymer Melts

• Published in: Physical review letters Vol. 121; no. 4; p. 047801
• Main Authors: O'Connor, Thomas C, Alvarez, Nicolas J, Robbins, Mark O
• Format: Journal Article
• Language: English
• Published: United States American Physical Society 27-07-2018
• Subjects: Chain entanglement; Confining; Crossovers; Deformation; Elongated structure; Entanglement; Melts; Molecular conformation; Molecular structure; Molecular weight; Polymer melts; Polymers; Trends; Viscosity
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/physrevlett.121.047801

Nonlinear extensional flows are common in polymer processing, but they 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 Wi_{R}=0.06-52 and Hencky strains ε≥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 Wi_{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.