Fast and Versatile Thermo-osmotic Flows with a Pinch of Salt

TL;DR

This paper develops a comprehensive model for thermo-osmotic flows in nanofluidic systems, demonstrating how surface properties and salt conditions can be tuned to generate large, controllable flows for waste heat harvesting.

Contribution

It introduces a general theoretical model for thermo-osmosis in charged nanofluidic channels, incorporating hydrodynamic slip and various solvent and solute effects.

Findings

Intense thermo-osmotic flows can be achieved with slipping charged surfaces.

Transition from thermophobic to thermophilic behavior depends on surface charge and salt concentration.

The model predicts controllable flow behavior using common charged surfaces and salt conditions.

Abstract

Thermo-osmotic flows - flows generated in micro and nanofluidic systems by thermal gradients - could provide an alternative approach to harvest waste heat. However, such use would require massive thermo-osmotic flows, which are up to now only predicted for special and expensive materials. There is thus an urgent need to design affordable nanofluidic systems displaying large thermo-osmotic coefficients. In this paper we propose a general model for thermo-osmosis of aqueous electrolytes in charged nanofluidic channels, taking into account hydrodynamic slip, together with the different solvent and solute contributions to the thermo-osmotic response. We apply this model to a wide range of systems, by studying the effect of wetting, salt type and concentration, and surface charge. We show that intense thermo-osmotic flows can be generated using slipping charged surfaces. We also predict for intermediate wettings a transition from a thermophobic to a thermophilic behavior depending on the surface charge and salt concentration. Overall, this theoretical framework opens an avenue for controlling and manipulating thermally induced flows with common charged surfaces and a pinch of salt.