Extensional Rheology of Neat and Contaminated Ring Polymer Melts

Molecular simulations are applied to study unconcatenated ring polymer melts in uniaxial extensional flow. Melts of neat rings and neat linear chains with the same length, and rings contaminated with a small fraction of linear chains are elongated to steady-state for a wide range of Rouse Weissenberg numbers. The rate dependence of the steady-state stress and viscosity are compared for the three systems and correlated with changes in microscopic chain conformations. Extensional flows stretch and orient both ring and linear chain conformations along the extension axis. However, linear chains can stretch to twice the length of a ring with the same molecular weight. The significantly stronger response of linear chains to extensional flow suggests a small fraction of linear chain contamination might dominate the extensional viscosity of a nominally neat ring melt. Simulations of ring melts contaminated with varying fractions of linear chains are used to predict the experimental signature of linear contamination.