  Interfacial hydrodynamic slippage of water depends on both on surface
chemistry and roughness. This study tries to connect the effect of chemical
property and the physical structure of the surface on the interfacial slippage
of water. By performing molecular dynamics simulations (MDS) of Couette flow of
water molecules over a reduced Lennard-Jones (LJ) surface, the velocity profile
is obtained and extrapolated to get the slip lengths. The slip lengths are
measured for various surface-fluid interactions. These interactions are varied
by changing the wettability of the surface (characterized by the static contact
angle) and its roughness. The slip length variation with the static contact
angle as $(1+cos\theta)^{-2}$ is observed. However, it is also observed that
the presence of surface roughness always reduces the slip length and it is
proposed that the slip length varies with non-dimensionalized average surface
roughness as $(1+\alpha^*)^{-2}$ . Thus a relation between the chemical
wettability and the physical roughness is established and their coupled
interactions modifying slip length is probed.
