Dynamically Heterogeneous Relaxation of Entangled Polymer Chains

TL;DR

This study investigates how individual entangled polymers relax after deformation, revealing dynamic heterogeneity with distinct relaxation modes linked to local disentanglement and reptation.

Contribution

It introduces single molecule techniques to observe relaxation in the transition from unentangled to entangled solutions, uncovering heterogeneous relaxation behaviors.

Findings

Identification of distinct relaxation modes including single and double exponential processes.

Correlation of the slow double-mode timescale with reptation dynamics.

Observation of transient local disentanglement affecting relaxation times.

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 unentangled to entangled solutions. 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. The slower double-mode timescale $\tau_{d,2}$ is consistent with a characteristic reptation time, whereas the single-mode timescale $\tau_s$ and the fast double-mode timescale $\tau_{d,1}$ are attributed to local regions of transient disentanglement due to deformation.