Dynamics of Fluid Mixtures in Nanospaces

TL;DR

This paper extends a microscopic theory to model the dynamics of multicomponent fluid mixtures in nanospaces, incorporating hydrodynamics, diffusion, and surface tension, and solves the equations numerically using a novel Lattice Boltzmann approach.

Contribution

It introduces a multicomponent extension of a microscopic fluid theory with a new Lattice Boltzmann implementation for confined fluid flows.

Findings

Validated the model with viscosity dependence on mixture composition.

Analyzed mixture dynamics in nanoslits and related structure to flow properties.

Demonstrated the model's ability to handle inhomogeneous, non-steady conditions.

Abstract

A multicomponent extension of our recent theory of simple fluids [ U.M.B. Marconi and S. Melchionna, Journal of Chemical Physics, 131, 014105 (2009) ] is proposed to describe miscible and immiscible liquid mixtures under inhomogeneous, non steady conditions typical of confined fluid flows. We first derive from a microscopic level the evolution equations of the phase space distribution function of each component in terms of a set of self consistent fields, representing both body forces and viscous forces (forces dependent on the density distributions in the fluid and on the velocity distributions). Secondly, we solve numerically the resulting governing equations by means of the Lattice Boltzmann method whose implementation contains novel features with respect to existing approaches. Our model incorporates hydrodynamic flow, diffusion, surface tension, and the possibility for global and local viscosity variations. We validate our model by studying the bulk viscosity dependence of the mixture on concentration, packing fraction and size ratio. Finally we consider inhomogeneous systems and study the dynamics of mixtures in slits of molecular thickness and relate structural and flow properties.