Slowing down of ring polymer diffusion caused by inter-ring threading

TL;DR

This study uses molecular dynamics simulations and a novel analysis method to demonstrate that threading interactions significantly slow down the diffusion of ring polymers in a melt, especially as polymer length increases.

Contribution

The paper introduces a new analysis approach to quantify threading dynamics in ring polymers and shows how threading causes diffusion slowdown with increasing polymerization.

Findings

Threading time increases more rapidly with polymer length than in linear polymers.

Threaded ring polymers require unthreading to diffuse, causing slowdowns.

Simulation results support threading as the main reason for diffusion slowdown.

Abstract

Diffusion of long ring polymers in a melt is much slower than the reorganization of their internal structures. While direct evidences for entanglements have not been observed in the long ring polymers unlike linear polymer melts, threading between the rings is suspected to be the main reason for slowing down of ring polymer diffusion. It is, however, difficult to define the threading configuration between two rings because the rings have no chain end. In this work, evidences for threading dynamics of ring polymers are presented by using molecular dynamics simulation and applying a novel analysis method. The simulation results are analyzed in terms of the statistics of persistence and exchange times that have proved useful in studying heterogeneous dynamics of glassy systems. We find that the threading time of ring polymer melts increases more rapidly with the degree of polymerization than that of linear polymer melts. This indicates that threaded ring polymers cannot diffuse until unthreading event occurs, which results in the slowing down of ring polymer diffusion.