Molecular scale contact line hydrodynamics of immiscible flows

TL;DR

This study uses molecular dynamics simulations to develop a continuum hydrodynamic model for immiscible two-phase flows, accurately capturing contact line behavior and interface breakup at the molecular scale.

Contribution

It introduces a continuum formulation incorporating a generalized Navier boundary condition based on molecular insights, bridging molecular dynamics and continuum hydrodynamics.

Findings

The generalized Navier boundary condition accurately describes slip at the contact line.

The continuum model matches molecular dynamics results for velocity and interfacial profiles.

The model predicts interface breakup at high capillary numbers.

Abstract

From extensive molecular dynamics simulations on immiscible two-phase flows, we find the relative slipping between the fluids and the solid wall everywhere to follow the generalized Navier boundary condition, in which the amount of slipping is proportional to the sum of tangential viscous stress and the uncompensated Young stress. The latter arises from the deviation of the fluid-fluid interface from its static configuration. We give a continuum formulation of the immiscible flow hydrodynamics, comprising the generalized Navier boundary condition, the Navier-Stokes equation, and the Cahn-Hilliard interfacial free energy. Our hydrodynamic model yields interfacial and velocity profiles matching those from the molecular dynamics simulations at the molecular-scale vicinity of the contact line. In particular, the behavior at high capillary numbers, leading to the breakup of the fluid-fluid interface, is accurately predicted.