Slip behavior in liquid films on surfaces of patterned wettability: Comparison between continuum and molecular dynamics simulations

Abstract

We investigate the behavior of the slip length in Newtonian liquids subject to planar shear bounded by substrates with mixed boundary conditions. The upper wall, consisting of a homogenous surface of finite or vanishing slip, moves at a constant speed parallel to a lower stationary wall, whose surface is patterned with an array of stripes representing alternating regions of no shear and finite or no slip. Velocity fields and effective slip lengths are computed both from molecular dynamics ͑MD͒ simulations and solution of the Stokes equation for flow configurations either parallel or perpendicular to the stripes. Excellent agreement between the hydrodynamic and MD results is obtained when the normalized width of the slip regions, a / տ O͑10͒, where is the ͑fluid͒ molecular diameter characterizing the Lennard-Jones interaction. In this regime, the effective slip length increases monotonically with a / to a saturation value. For a / Շ O͑10͒ and transverse flow configurations, the nonuniform interaction potential at the lower wall constitutes a rough surface whose molecular scale corrugations strongly reduce the effective slip length below the hydrodynamic results. The translational symmetry for longitudinal flow eliminates the influence of molecular scale roughness; however, the reduced molecular ordering above the wetting regions of finite slip for small values of a / increases the value of the effective slip length far above the hydrodynamic predictions. The strong correlation between the effective slip length and the liquid structure factor representative of the first fluid layer near the patterned wall illustrates the influence of molecular ordering effects on slip in noninertial flows.

Effective slip and friction reduction in nanograted superhydrophobic microchannels

“…Fluids 18, 087105 ͑2006͒ due to the minute variation of nanograte geometries from sample to sample; potential discrepancy between theory and experiment͒, our experimental results agree well with the continuum hydrodynamic analysis. Furthermore, our testing results confirm the prediction 28,36,[41][42][43] that a flow transverse to the grating pattern would have a smaller effective slip than would a flow parallel to the grating. In transverse flows, the flow field near the wall constantly develops, repeatedly encountering a region of fluid over a trough and a region of solid on a grating peak; this entails a higher pressure drop overall.…”

Depletion at solid/liquid interfaces: Flowing hexadecane on functionalized surfaces

“…8 and 9. Such surface-induced order under shear stress has already been observed in the case of micelles 30, 31 using neutron scattering and indirectly in confined propanol 10 and eicosane 11 using SFA and AFM based techniques, as well as in MD simulations 32 and theoretical calculations 33 of confined liquids.…”

Superhydrophobic drag reduction in laminar flows: a critical review

“…Following early work (Philip 1972a, b), many analytical models about slip lengths on simple SHPo surfaces have been developed (Lauga and Stone 2003;Ybert et al 2007;Sbragaglia and Prosperetti 2007a, b;Davis and Lauga 2009a, b;Feuillebois et al 2009;Belyaev and Vinogradova 2010a, b;Davis and Lauga 2010;Asmolov and Vinogradova 2012;Cottin-Bizonne et al 2012) and corroborated by numerical simulations (Cottin-Bizonne et al 2003Priezjev et al 2005;Hendy and Lund 2007;Biben and Joly 2008;Hyvalouma and Harting 2008;Teo and Khoo 2008;Cheng et al 2009;Wang 2009, 2010;Teo and Khoo 2010). By fabricating near-perfect microstructures in an extremely clean condition, Lee et al (2008) succeeded to measure the slip length as a function of surface features, finally verifying the early theoretical models (Lauga and Stone 2003;Ybert et al 2007) quantitatively and bringing a conclusion to the issue.…”