Amit Varakhedkar | Searcharxiv

arXiv2026

Linear Viscoelasticity of Semidilute Unentangled Flexible Polymer Solutions

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. In the dilute limit, simulations recover 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 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 due to finite-chain discretization effects. Systematic accounting for these finite-chain length effects using successive fine-graining enables quantitative prediction of the loss modulus in the infinite-chain length limit.

cond-mat.soft↗

arXiv2025

Linear Viscoelasticity of Semiflexible Polymers with Hydrodynamic Interactions

The linear viscoelastic response of single semiflexible polymer chains in the infinite-dilution limit is studied using Brownian dynamics simulations of coarse-grained bead-spring chains. The springs obey the FENE-Fraenkel force law, a bending potential is used to capture chain stiffness and hydrodynamic interactions are included through the Rotne-Prager-Yamakawa tensor. By calculating the relaxation modulus following a step strain, we demonstrate that the bead-spring chain behaves like an inextensible semiflexible rod over a wide time window with an appropriate choice of spring stiffness and chain extensibility. In the absence of hydrodynamic interactions, our results agree with the existing theoretical predictions for the linear viscoelastic response of free-draining, inextensible, semiflexible rods in the limit of infinite dilution. It is shown that at intermediate times, the stress relaxation modulus exhibits power law behaviour, with the exponent ranging from $(-1/2)$ for flexible chains to $(-5/4)$ for highly rigid chains. At long times, rigid chains undergo orientational relaxation, while flexible chains exhibit Rouse relaxation. Hydrodynamic interactions are found to effect the behaviour at intermediate and long times, with the difference from free-draining behaviour increasing with increasing chain flexibility. Computations of the frequency dependence of loss and storage moduli are found to be in good agreement with experimental data for a wide variety of systems involving semiflexible polymers of varying stiffness across a broad frequency range.

cond-mat.soft↗