Dynamics of simple liquids at heterogeneous surfaces: Molecular-dynamics simulations and hydrodynamic description
Laboratoire de Physique de la Matière Condensée et Nanostructures, CNRS and Université Lyon I, 43 Boulevard du 11 Novembre, 69622, Villeurbanne Cedex, France
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Accepted: 15 October 2004
Published online: 20 December 2004
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 super-hydrophobic 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 at the composite interface. Comparison between the two approaches shows that they 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.
PACS: 68.15.+e Liquid thin films – / 83.50.Rp Wall slip and apparent slip – / 68.08.-p Liquid-solid interfaces –
© EDP Sciences, Società Italiana di Fisica and Springer-Verlag, 2005