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

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 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.

Slippage of Water Past Superhydrophobic Carbon Nanotube Forests in Microchannels

“…This confirms recent theoretical predictions made for the effective slip length on superhydrophobic microstructured surfaces [9][10][11][12]. In the Cassie state, the liquid is in direct contact with the solid only through a small fraction ( S ) of the surface.…”

“…As shown in Fig. 4, slippage is strongly reduced in the Wenzel state, due to the increased liquid-solid friction in the absence of trapped air in the CNT, in agreement with theoretical predictions [11].…”

Superhydrophobic drag reduction in laminar flows: a critical review

“…Reynolds number (Cheng et al 2009;Hyvalouma and Harting 2008), a confinement condition (the channel height being much smaller than the free surface distance between structures) (Philip 1972a;Sbragaglia and Prosperetti 2007a), and a slip on solid patches (Choi et al 2006;Cottin-Bizonne et al 2004;Hendy and Lund 2007;Ybert et al 2007) can affect slip lengths under certain conditions.…”

Non-Local Scattering Kernel and the Hydrodynamic Limit

“…4 and Sect. 5 where we propose a model for the interaction of fluid particles with a wall which, we believe, can be of interest in micro and nano-fluidics.…”

“…It is impossible here to review the relevant literature on MD and we refer e.g. to [4,6,7,14,15] and to references therein. Our approach, being based on kinetic theory, is mesoscopic, in the same spirit of [3] where the Lattice Boltzmann Equation is considered.…”