Fluid flow at interfaces driven by thermal gradients

TL;DR

This paper develops a microscopic linear response theory for thermo-osmosis, explaining how thermal gradients induce fluid flow at interfaces, and validates some predictions with molecular dynamics simulations.

Contribution

It provides a complete derivation of the microscopic theory of thermo-osmosis and applies it to confined fluids, including both open and closed channel scenarios.

Findings

Successful prediction validation via molecular dynamics simulations

Quantitative evaluation of generalized transport coefficients

Application to fluid flow through membrane-like geometries

Abstract

Thermal forces drive several nonequilibrium phenomena able to set a fluid in motion without pressure gradients. Although the most celebrated effect is thermophoresis, also known as Ludwig-Soret effect, probably the simplest example where thermal forces are at play is thermo-osmosis: The motion of a {\it confined} fluid exclusively due to the presence of a temperature gradient. We present a concise but complete derivation of the microscopic theory of thermo-osmosis based on linear response theory. This approach is applied to a simple fluid confined in a slab geometry, mimicking the flow through a pore in a membrane separating two fluid reservoirs at different temperatures. We consider both the case of an open channel, where the fluid can flow freely, and that of a closed channel, where mass transport is inhibited and a pressure drop sets in at the boundaries. Quantitative results require the evaluation of generalized transport coefficients, but a preliminary check on a specific prediction of the theory has been successfully performed via nonequilibrium molecular dynamics simulations.