Thermal diffusion by Brownian motion induced fluid stress

TL;DR

This study combines Brownian dynamics and lattice Boltzmann simulations to investigate the Ludwig-Soret effect, revealing how thermal stress gradients induce particle migration in fluids, with results aligning with experimental data.

Contribution

It provides a detailed simulation-based explanation of thermal diffusion caused by fluid stress gradients, advancing understanding of the Ludwig-Soret effect.

Findings

DNA migrates to colder regions in thermal gradients

Thermal diffusion coefficient decreases with particle size

Fluid stress gradients drive thermal migration

Abstract

The Ludwig-Soret effect, the migration of a species due to a temperature gradient, has been extensively studied without a complete picture of its cause emerging. Here we investigate the dynamics of DNA and spherical particles sub jected to a thermal gradient using a combination of Brownian dynamics and the lattice Boltzmann method. We observe that the DNA molecules will migrate to colder regions of the channel, an observation also made in the experiments of Duhr, et al[1]. In fact, the thermal diffusion coefficient found agrees quantitatively with the experimental value. We also observe that the thermal diffusion coefficient decreases as the radius of the studied spherical particles increases. Furthermore, we observe that the thermal fluctuations-fluid momentum flux coupling induces a gradient in the stress which leads to thermal migration in both systems.