Mapping molecular models to continuum theories for partially miscible fluids

TL;DR

This paper develops a comprehensive mapping from molecular dynamics simulations of partially miscible fluid interfaces to mesoscale continuum models, revealing limitations of common assumptions and improving model accuracy at near-molecular scales.

Contribution

It introduces a detailed mapping methodology that includes stress profiles, improving mesoscale models' fidelity to molecular dynamics data for fluid interfaces.

Findings

Incompressibility assumptions fail at interfaces, affecting surface tension.

Consistent parameterization reduces spurious velocities in mesoscale models.

The improved model matches molecular dynamics results at near-molecular interface widths.

Abstract

We map molecular dynamics simulations of fluid-fluid interfaces onto mesoscale continuum theories for partially miscible fluids. Unlike most previous work, we examine not only the interface order parameter and density profiles, but also the stress. This allows a complete mapping from the length scales of molecular dynamics simulations onto a mesoscale model suitable for a lattice Boltzmann or other mesoscale simulation method. Typical assumptions of mesoscale models, such as incompressibility, are found to fail at the interface, and this has a significant impact on the surface tension. Spurious velocities, found in a number of discrete models of curved interfaces, are found to be minimized when the parameters of the mesoscopic model are made consistent with molecular dynamics results. An improved mesoscale model is given and demonstrated to produce results consistent with molecular dynamics simulations for interfaces with widths down to near molecular size.