What controls thermo-osmosis? Molecular simulations show the critical role of interfacial hydrodynamics

TL;DR

This study uses molecular dynamics simulations to uncover how nanoscale interfacial hydrodynamics influence thermo-osmotic phenomena, highlighting the effects of surface wetting properties and interfacial friction on thermo-osmotic transport.

Contribution

The paper demonstrates the critical role of interfacial hydrodynamics in thermo-osmosis, revealing how slip and shear plane position affect transport coefficients, with implications for interface design.

Findings

Hydrodynamic slip amplifies thermo-osmotic transport on non-wetting surfaces.

The shear plane position determines the sign and magnitude of thermo-osmosis on wetting surfaces.

Water-graphene interface exhibits a giant thermo-osmotic response due to low interfacial friction.

Abstract

Thermo-osmotic and related thermo-phoretic phenomena can be found in many situations from biology to colloid science, but the underlying molecular mechanisms remain largely unexplored. Using molecular dynamics simulations, we measured the thermo-osmosis coefficient by both mechano-caloric and thermo-osmotic routes, for different solid-liquid interfacial energies. The simulations reveal in particular the crucial role of nanoscale interfacial hydrodynamics. For non-wetting surfaces , thermo-osmotic transport is largely amplified by hydrodynamic slip at the interface. For wetting surfaces, the position of the hydrodynamic shear plane plays a key role in determining the amplitude and sign of the thermo-osmosis coefficient. Finally, we measure a giant thermo-osmotic response of the water-graphene interface, which we relate to the very low interfacial friction displayed by this system. These results open new perspectives for the design of efficient functional interfaces for, e.g., waste heat harvesting.