Effects of hydrodynamic noise on the diffusion of polymers in dilute solutions

TL;DR

This paper extends the Rouse-Zimm model for polymer diffusion by incorporating hydrodynamic noise and viscous aftereffects, revealing how noise influences polymer dynamics and diffusion coefficients.

Contribution

It introduces a generalized Rouse-Zimm equation accounting for hydrodynamic noise and viscous effects, linking noise correlations to polymer diffusion behavior.

Findings

Velocity autocorrelation follows t^(-3/2) law at long times.

Diffusion coefficient aligns with Zimm theory with size-dependent corrections.

Hydrodynamic noise significantly impacts polymer diffusion characteristics.

Abstract

The Rouse-Zimm equation for the position vectors of beads mapping the polymer is generalized by taking into account the viscous aftereffect and the hydrodynamic noise. For the noise, the random fluctuations of the hydrodynamic tensor of stresses are responsible. The preaveraging of the Oseen tensor for the nonstationary Navier-Stokes equation allowed us to relate the time correlation functions of the Fourier components of the bead position to the correlation functions of the hydrodynamic field created by the noise. The velocity autocorrelation function of the center of inertia of the polymer coil is considered in detail for both the short and long times when it behaves according to the t^(-3/2) law and does not depend on any polymer parameters. The diffusion coefficient of the polymer is close to that from the Zimm theory, with corrections depending on the ratio between the size of the bead and the size of the whole coil.