Chain motion and viscoelasticity in highly entangled solutions of semiflexible rods

TL;DR

This study uses Brownian dynamics simulations to explore how entanglement influences the motion and viscoelastic properties of semiflexible polymers, revealing a concentration threshold where behavior shifts significantly.

Contribution

The paper introduces a detailed simulation analysis showing the concentration-dependent transition in bending fluctuations and viscoelastic response of semiflexible rods.

Findings

Entanglement affects bending fluctuations above a critical concentration c**.

Tube radius R_e scales as c^{-3/5} for c > c**.

Viscoelastic response becomes elastic above c**.

Abstract

Brownian dynamics simulations are used to study highly entangled solutions of semiflexible polymers. Bending fluctuations of semiflexible rods are signficantly affected by entanglement only above a concentration $c^{**}$, where $c^{**}\sim 10^{3}L^{-3}$ for chains of similar length $L$ and persistence length. For $c > c^{**}$, the tube radius $R_{e}$ approaches a dependence $R_{e} \propto c^{-3/5}$, and the linear viscoelastic response develops an elastic contribution that is absent for $c < c^{**}$. Experiments on isotropic solutions of $F$-actin span concentrations near $c^{**}$ for which the predicted asymptotic scaling of the plateau modulus $G \propto c^{7/5}$ is not yet valid.