Complex coupling between surface charge and thermo-osmotic phenomena

TL;DR

This study investigates how surface charge distribution influences thermo-osmotic flows and electric currents at liquid-solid interfaces, revealing complex coupling effects crucial for optimizing waste heat recovery systems.

Contribution

It provides new insights into the impact of surface charge distribution on interfacial enthalpy excess and thermo-osmotic phenomena using molecular dynamics simulations and analytical models.

Findings

Surface charge significantly affects interfacial enthalpy excess.

Dependence of enthalpy excess on charge distribution varies with surface conditions.

Wetting has minimal impact on charge-enthalpy coupling.

Abstract

Thermo-osmotic flows, generated at liquid-solid interfaces by thermal gradients, can be used to produce electric currents from waste heat on charged surfaces. The two key parameters controlling the thermo-osmotic current are the surface charge and the interfacial enthalpy excess due to liquid-solid interactions. While it has been shown that the contribution from water to the enthalpy excess can be crucial, how this contribution is affected by surface charge remained to be understood. Here, we start by discussing how thermo-osmotic flows and induced electric currents are related to the interfacial enthalpy excess. We then use molecular dynamics simulations to investigate the impact of surface charge on the interfacial enthalpy excess, for different distributions of the surface charge, and two different wetting conditions. We observe that surface charge has a strong impact on enthalpy excess, and that the dependence of enthalpy excess on surface charge depends largely on its distribution. In contrast, wetting has a very small impact on the charge-enthalpy coupling. We rationalize the results with simple analytical models, and explore their consequences for thermo-osmotic phenomena. Overall, this work provides guidelines to search for systems providing optimal waste heat recovery performance.