Reaction kinetics of coarse-grained equilibrium polymers: a Brownian Dynamics study

TL;DR

This study uses Brownian Dynamics simulations to analyze the reaction kinetics of equilibrium polymers, revealing how chain dynamics depend on reaction attempt frequency and identifying the limitations of simple kinetic theories at short times.

Contribution

A new mesoscopic Brownian Dynamics model for equilibrium polymers that incorporates reversible binding/unbinding and elucidates chain reaction kinetics in dilute to semi-dilute regimes.

Findings

Reaction kinetics depend on the attempt frequency parameter.

Simple kinetic theories are valid for times longer than the average chain lifetime.

Strong dynamical correlations are observed at short times.

Abstract

Self-assembled linear structures like giant cylindrical micelles or discotic molecules in solution stacked in flexible columns are systems reminiscent of polydisperse polymer solutions.These supramolecular polymers have an equilibrium length distribution, the result of a competition between the random breakage of chains and the fusion of chains to generate longer ones. In the present work, we review the basic theoretical concepts of these ``equilibrium polymers" and some of the important results obtained by simulation approaches. We propose a new version of a mesoscopic model in continuous space based on the bead and FENE spring polymer model which is treated by Brownian Dynamics and Monte-Carlo binding/unbinding reversible changes for adjacent monomers in space, characterized by an attempt frequency parameter. For a dilute and a moderately semi-dilute state-points which both correspond to dynamically unentangled regimes, the dynamic properties are found to depend upon $\omega$ through the effective life time $\tau_b$ of the average size chain which, in turn, yields the kinetic reaction coefficients of the mean-field kinetic model proposed by Cates. Simple kinetic theories seem to work for times $ t \geq \tau_b$ while at shorter time, strong dynamical correlation effects are observed.