Contribution of internal degree of freedom of soft molecules to Soret effect

TL;DR

This study uses molecular dynamics simulations to explore how the internal flexibility of soft molecules influences the Soret effect, revealing that increased softness alters the thermal diffusion behavior and can reverse the direction of molecular migration.

Contribution

It introduces a detailed analysis of the internal degrees of freedom's impact on the Soret effect, highlighting mechanisms behind the observed changes in thermal diffusion.

Findings

Thermal diffusion factor decreases with molecule softness.

Sign change in the Soret effect observed as molecules become softer.

Flexible molecules tend to migrate differently compared to rigid ones.

Abstract

We studied the Soret effect in binary dimer-monomer mixtures using non-equilibrium molecular dynamics simulations and investigated the pure contribution of the internal degree of freedom of flexible molecules to the Soret effect. We observed that the thermal diffusion factor tends to decrease and change its sign as the molecules become softer. We proposed two possible mechanisms of our observations: change of the molecule structures with the temperature, causing bulkier molecules to migrate to the hotter region; asymmetry of the restitution between rigid and flexible molecules, due to which flexible molecules show larger restitution when placed at the hotter region.