Linear Viscoelasticity of Semidilute Unentangled Flexible Polymer Solutions

TL;DR

This study uses Brownian dynamics simulations to analyze the linear viscoelastic behavior of flexible polymer solutions in dilute and semidilute unentangled regimes, connecting microscopic dynamics to macroscopic response.

Contribution

It provides a detailed simulation-based analysis of viscoelastic properties across concentration regimes, incorporating finite-chain effects with the successive fine-graining technique.

Findings

Simulations recover Zimm-like behavior in dilute solutions.

Crossover to Rouse-like dynamics observed with increasing concentration.

Excellent agreement with experimental data for storage modulus.

Abstract

The linear viscoelastic response of flexible polymer solutions in the dilute and semidilute unentangled regimes is investigated using Brownian dynamics simulations. The relaxation modulus and dynamic moduli are computed over a wide range of concentrations and chain discretizations for both $\theta$ and good solvents to establish the connection between microscopic chain dynamics and macroscopic viscoelastic response. In the dilute limit, the simulations recover the expected Zimm-like behavior with solvent-quality-dependent power-law scaling in the intermediate time and frequency regimes, while in the semidilute unentangled regime a systematic crossover to Rouse-like dynamics is observed with increasing concentration due to the screening of excluded volume and hydrodynamic interactions. Comparison with experimental measurements shows excellent agreement for the storage modulus across both concentration regimes and for the loss modulus at low and intermediate frequencies, with deviations at high frequencies as a result of finite-chain discretization effects. These finite-chain length effects are systematically accounted for using the successive fine-graining technique, enabling quantitative prediction of the loss modulus in the infinite-chain length limit.