EPJ E Colloquium - Predicting thermodiffusion in simple binary fluid mixtures

Details

Published on 14 June 2022

When a homogeneous mixture is subjected to a thermal gradient, the fluid components are partially separated because of the temperature gradient. This phenomenon, known since the mid-19th century, is called thermodiffusion, the Soret effect or thermophoresis. Despite its relatively small amplitude it impacts many natural systems, such as the salinity gradient in ocean or even pre-biological evolution, and can be exploited in applications ranging from the manipulation of biological macromolecules to isotope enrichment. However, despite numerous attempts by leading researchers, including some Nobel laureates, a full understanding of the microscopic origin of this subtle phenomenon is still lacking and there is no consensus on which model, among the numerous existing ones, is the most reliable to quantify it in dense phases.

In a new Colloquium published in EPJE, the capability of some theoretical models to predict the thermal diffusion factor of simple binary mixtures over a wide range of thermodynamic conditions has been systematically investigated. To do so, tests have been performed via extensive molecular simulations using the Hard-Sphere and the Lennard-Jones (including spheres and dimers) models. It has been found that none of the existing models was able to quantify thermodiffusion in all cases, in particular when the involved species in the mixtures present an asymmetry in size or in shape. To go further, based on these molecular simulations results, some guidelines have been provided to develop a new model to predict thermodiffusion in simple fluid mixtures. Reaching such a point is probably now realistic and would greatly improve our current understanding of many natural fluid systems.