How important are fluctuations in the treatment of internal friction in polymers?

TL;DR

This paper critically examines the Rouse model with internal friction, revealing that its preaveraged approximation may lead to inaccuracies, especially for short chain segments and out-of-equilibrium conditions like shear flow.

Contribution

It compares the traditional preaveraged Rouse model with an exact coarse-grained model incorporating fluctuations, highlighting the limitations of the former.

Findings

Preaveraged model aligns with exact model for long chain segments.

Differences observed in short segments and out-of-equilibrium predictions.

Preaveraging may oversimplify internal friction effects in polymers.

Abstract

The Rouse model with internal friction (RIF), a widely used theoretical framework to interpret the effects of internal friction on conformational transitions in biomolecules, is shown to be an approximate treatment that is based on preaveraging internal friction. By comparison with Brownian dynamics simulations of an exact coarse-grained model that incorporates fluctuations in internal friction, the accuracy of the preaveraged model predictions is examined both at and away from equilibrium. While the two models predict intrachain autocorrelations that approach each other for long enough chain segments, they differ in their predictions for shorter segments. Furthermore, the two models differ qualitatively in their predictions for the chain extension and viscosity in shear flow, which is taken to represent a prototypical out-of-equilibrium condition.