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Published April 1, 2005 | public
Journal Article Open

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


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 (MD) 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/sigma>~O(10), where sigma is the (fluid) molecular diameter characterizing the Lennard-Jones interaction. In this regime, the effective slip length increases monotonically with a/sigma to a saturation value. For a/sigma<~O(10) 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/sigma 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.

Additional Information

©2005 The American Physical Society (Received 7 October 2004; published 27 April 2005) The authors kindly acknowledge financial support from the National Science Foundation, the NASA Microgravity Fluid Physics Program, and the U.S. Army TACOM ARDEC. N.V.P. would like to thank J. Rottler for useful discussions. S.M.T. gratefully acknowledges the support and generous hospitality of the Moore Distinguished Scholar Program at the California Institute of Technology.


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