Uniaxial Elongational Flow of Ring-Polymer Melts with Associating Groups

John Bracewell
Clemson University
Gary S. Grest
Sandia National Laboratories
Thomas C. O’Connor
Carnegie Mellon
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Recent studies of effects of uniaxial extensional flows on linear polymers, driven by polymer processing challenges, have raised several fundamental questions regarding the impact of entanglements. Non-concatenated ring polymers, which have no free ends, do not entangle like linear polymers, thus serve as an excellent model for understanding flow response. Previous studies found that links formed spontaneously in the ring system under extensional flow, which led to the unexpected large increases in extensional viscosity observed experimentally. Associating groups were added to the bead-spring model to determine their effect on the formation of these topological links. The fraction of associating groups was varied from 2% to 10%, and association strength was varied from 1–10kBT. As for linear chains, the associating groups form clusters, which increase in size as the strength of the associating groups increase. These clusters are dynamic under flow, continuously breaking up and reforming. They govern the distribution of ring extensions which become heterogeneous for strongly interacting associating groups. Even for large interaction strength, some rings still form topological links, in which case the viscosity is due to a combination of these linked rings and the associating groups.