Crossover Time in Relative Fluctuations Characterizes the Longest Relaxation Time of Entangled Polymers

TL;DR

This paper introduces a novel relative fluctuation analysis method to accurately determine the longest relaxation time of entangled polymers from simulation data, providing a new approach to understanding polymer dynamics.

Contribution

The paper presents a new fluctuation analysis technique to identify the longest relaxation time in entangled polymers from center of mass trajectories.

Findings

The method accurately estimates the longest relaxation time as a crossover in relative fluctuations.

Application to simulation models confirms the method's effectiveness.

Provides a new tool for analyzing polymer relaxation dynamics.

Abstract

In entangled polymer systems, there are several characteristic time scales, such as the entanglement time and the disengagement time. In molecular simulations, the longest relaxation time (the disengagement time) can be determined by the mean square displacement (MSD) of a segment or by the shear relaxation modulus. Here, we propose the relative fluctuation analysis method, which is originally developed for characterizing large fluctuations, to determine the longest relaxation time from the center of mass trajectories of polymer chains (the time-averaged MSDs). Applying the method to simulation data of entangled polymers (by the slip-spring model and the simple reptation model), we provide a clear evidence that the longest relaxation time is estimated as the crossover time in the relative fluctuations.