Pressure Gradients Fail to Predict Diffusio-Osmosis

TL;DR

This study evaluates different computational methods for predicting diffusio-osmotic flow, finding that chemical potential gradient-based approaches align with direct simulations, while stress tensor gradient methods do not.

Contribution

The paper compares multiple approaches for modeling diffusio-osmotic flow and confirms the validity of chemical potential gradient methods over stress tensor gradient methods.

Findings

Chemical potential gradient approach agrees with direct simulations.

Stress tensor gradient approach does not match direct simulation results.

Supports the use of chemical potential gradients for accurate diffusio-osmotic flow prediction.

Abstract

We present numerical simulations of diffusio-osmotic flow, i.e. the fluid flow generated by a concentration gradient along a solid-fluid interface. In our study, we compare a number of distinct approaches that have been proposed for computing such flows and compare them with a reference calculation based on direct, non-equilibrium Molecular Dynamics simulations. As alternatives, we consider schemes that compute diffusio-osmotic flow from the gradient of the chemical potentials of the constituent species and from the gradient of the component of the stress tensor parallel to the interface. We find that the approach based on treating chemical potential gradients as external forces acting on various species agrees with the direct simulations, thereby supporting the approach of Marbach et al. (J Chem Phys 146, 194701 (2017)). In contrast, an approach based on computing the gradients of the microscopic pressure tensor does not reproduce the direct non-equilibrium results.