The influence of periodic and random surface textures on the flow structure
and effective slip length in Newtonian fluids is investigated by molecular
dynamics (MD) simulations. We consider a situation where the typical pattern
size is smaller than the channel height and the local boundary conditions at
wetting and nonwetting regions are characterized by finite slip lengths. In
case of anisotropic patterns, transverse flow profiles are reported for flows
over alternating stripes of different wettability when the shear flow direction
is misaligned with respect to the stripe orientation. The angular dependence of
the effective slip length obtained from MD simulations is in good agreement
with hydrodynamic predictions provided that the stripe width is larger than
several molecular diameters. We found that the longitudinal component of the
slip velocity along the shear flow direction is proportional to the interfacial
diffusion coefficient of fluid monomers in that direction at equilibrium. In
case of random textures, the effective slip length and the diffusion
coefficient of fluid monomers in the first layer near the heterogeneous surface
depend sensitively on the total area of wetting regions.Comment: 30 pages, 11 figure