Dynamics of simple liquids at heterogeneous surfaces : Molecular Dynamics simulations and hydrodynamic description

TL;DR

This study combines molecular dynamics simulations and hydrodynamic modeling to analyze how surface heterogeneity influences fluid slip behavior, revealing that small surface roughness variations can significantly enhance slip, with implications for microfluidic surface design.

Contribution

It introduces a combined MD and hydrodynamic approach to quantify slip on heterogeneous surfaces and provides guidelines for designing highly slippery surfaces.

Findings

Superhydrophobic state leads to large slip in MD simulations.

Hydrodynamic estimates agree with MD results at low pressure.

Surface roughness variations greatly affect slip behavior.

Abstract

In this paper we consider the effect of surface heterogeneity on the slippage of fluid, using two complementary approaches. First, MD simulations of a corrugated hydrophobic surface have been performed. A dewetting transition, leading to a super-hydrophobic state, is observed for pressure below a ``capillary'' pressure. Conversely a very large slippage of the fluid on this composite interface is found in this superhydrophobic state. Second, we propose a macroscopic estimate of the effective slip length on the basis of continuum hydrodynamics, in order to rationalize the previous MD results. This calculation allows to estimate the effect of a heterogeneous slip length pattern on the composite interface. Comparison between the two approaches are in good agreement at low pressure, but highlights the role of the exact shape of the liquid-vapor interface at higher pressure. These results confirm that small variations in the roughness of a surface can lead to huge differences in the slip effect. On the basis of these results, we propose some guidelines to design highly slippery surfaces, motivated by potential applications in microfluidics.