# Osmotic and diffusio-osmotic flow generation at high solute concentration. II. Molecular dynamics simulations

## TL;DR

This study uses molecular dynamics simulations to investigate osmotic and diffusio-osmotic flows at high solute concentrations, introducing a novel NEMD method validated against theory and applied to water-ethanol mixtures near solid surfaces.

## Contribution

It presents a new non-equilibrium MD methodology for simulating diffusion-osmosis driven by chemical potential gradients.

## Key findings

- Validated NEMD method matches linear-response theory.
- Analyzed osmotic reflection coefficient at various concentrations.
- Applied framework to water-ethanol mixtures on silica and graphene surfaces.

## Abstract

In this paper, we explore osmotic transport by means of molecular dynamics (MD) simulations. We first consider osmosis through a membrane, and investigate the reflection coefficient of an imperfectly semi-permeable membrane, in the dilute and high concentration regimes. We then explore the diffusion-osmotic flow of a solute-solvent fluid adjacent to a solid surface, driven by a chemical potential gradient parallel to the surface. We propose a novel non-equilibrium MD (NEMD) methodology to simulate diffusion-osmosis, by imposing an external force on every particle, which properly mimics the chemical potential gradient on the solute in spite of the periodic boundary conditions. This NEMD method is validated theoretically on the basis of linear-response theory by matching the mobility with their Green-Kubo expressions. Finally, we apply the framework to more realistic systems, namely a water-ethanol mixture in contact with a silica or a graphene surface.