Hydrodynamic slip boundary condition at chemically patterned surfaces: A continuum deduction from molecular dynamics

TL;DR

This paper derives a continuum hydrodynamic model with a variable slip length for flow over chemically patterned surfaces, validated by molecular dynamics simulations, enabling control of slip properties in nanofluidic applications.

Contribution

It develops a continuum model with a spatially varying slip length based on MD data, confirming the Navier slip condition on chemically patterned surfaces.

Findings

Continuum model agrees quantitatively with MD simulations.

Surface patterning can tune the effective slip length.

Small pattern periods lead to homogeneous slip behavior.

Abstract

We investigate the slip boundary condition for single-phase flow past a chemically patterned surface. Molecular dynamics (MD) simulations show that modulation of fluid-solid interaction along a chemically patterned surface induces a lateral structure in the fluid molecular organization near the surface. Consequently, various forces and stresses in the fluid vary along the patterned surface. Given the presence of these lateral variations, a general scheme is developed to extract hydrodynamic information from MD data. With the help of this scheme, the validity of the Navier slip boundary condition is verified for the chemically patterned surface, where a local slip length can be defined. Based on the MD results, a continuum hydrodynamic model is formulated using the Navier-Stokes equation and the Navier boundary condition, with a slip length varying along the patterned surface. Steady-state velocity fields from continuum calculations are in quantitative agreement with those from MD simulations. It is shown that, when the pattern period is sufficiently small, the solid surface appears to be homogeneous, with an effective slip length that can be controlled by surface patterning. Such a tunable slip length may have important applications in nanofluidics.