Thermophoresis from first principles

• Applicant: Dr. Aljaz Godec
• Subject Area: Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 431945604

Thermophoresis, also known as the Ludwig-Soret effect, stands for the diffusive transport of matter induced by a temperature gradient. It is a general phenomenon, observed in the gaseous, fluid, and solid states (even within nanotubes), and has important technological applications, especially in energy harvesting, conversion, and storage, as well as in biotechnology. Despite the vast variety of applications and notwithstanding intensive research in the field (including classical (equilibrium) thermodynamics, Onsager’s Theory, non-isothermal fluctuating hydrodynamics, etc.), a microscopic understanding of the origin of thermophoretic transport far from thermodynamic equilibrium from the perspective of statistical mechanics of individual particles remains elusive. In particular, the actual interplay between the non-equilibrium fluctuations in the heat-current-carrying medium and the interactions between a tracer particle and the medium particles, which is responsible for the symmetry breaking deciding the direction of the transport (along or against the temperature gradient), as well as the precise conditions required for the timescale separations typically presumed in existing phenomenological approaches are still poorly understood. In the present project we will investigate thermophoresis from a first-principles perspective, starting from Newtonian mechanics of a tracer coupled to an explicit, particle-resolved medium driven into a non-equilibrium, heat-current-carrying steady state. We will focus on the transport properties and the (generally strong-coupling) stochastic thermodynamics of the phenomenon, especially the symmetry breaking the fluctuations of the medium and the temperature dependence of the Soret coefficient beyond the linear (Onsager) regime. We will combine a systematic rigorous analysis of the equations of motion arising from continuum limit of the bath and a subsequent systematic elimination of the bath-degrees of freedom with extensive nonequilibrium Molecular Dynamics simulations with thermostated boundary regions.

• DFG Programme: Research Units
• Subproject of: FOR 5099: Reducing complexity of nonequilibrium systems
• Co-Investigator: Professor Dr. Joachim Dzubiella