Paper Number
PS9 

Session
Polymers in Solution

Title
Entangled polymer chains relax via dynamically heterogeneous pathways

Presentation Date and Time
October 15, 2018 (Monday) 2:45

Track / Room
Track 4 / Post Oak

Authors (Click on name to view author profile)

1. Zhou, Yuecheng (University of Illinois at Urbana-Champaign, Materials Science and Engineering)
2. Schroeder, Charles M. (University of Illinois at Urbana-Champaign, Chemical and Biomolecular Engineering)

Author and Affiliation Lines (in printed abstract book)
Yuecheng Zhou¹ and Charles M. Schroeder^2
1Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801; ²Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Speaker / Presenter 
Schroeder, Charles M.

Text of Abstract
Stress relaxation following deformation of an entangled polymeric liquid is thought to be affected by transient reforming of chain entanglements. In this work, we use single molecule techniques to study the relaxation of individual polymers in the transition regime from semi-dilute unentangled to entangled solutions. In particular, we directly observe the relaxation dynamics of linear tracer polymers in background solutions of linear entangled polymers across a wide range of concentrations spanning c_e < c < c**. Our results reveal the emergence of dynamic heterogeneity underlying polymer relaxation behavior, including distinct molecular sub-populations described by a single-mode and a double-mode exponential relaxation process. Interestingly, this dynamic behavior starkly contrasts polymer relaxation in dilute and semi-dilute unentangled solutions. As polymer concentration is increased from ~3 c* to ~15 c* (spanning ~1 c_e to ~5 c_e), the fraction of molecules that exhibit single-mode exponential decay behavior decreases, whereas the fraction of double-mode exponential trajectories increases, with nearly all relaxation trajectories showing a double exponential response at high concentrations. In all cases, we interpret the power law scaling of these characteristic relaxation times as a function of concentration. The slower double-mode timescale is consistent with a characteristic reptation time, whereas the single-mode timescale and the fast double-mode timescale are attributed to local regions of transient disentanglement due to deformation. These results are discussed and rationalized in the context of existing molecular and phenomenological models of entangled polymer solutions such as the classic tube model and recent extensions. Taken together, these results reveal fundamentally new information regarding the behavior of polymer chain relaxation for lightly entangled solutions.