Viscous flow over a chemically patterned surface.

The classical fluid dynamics boundary condition of no slip suggests that variation in the wettability of a solid should not affect the flow of an adjacent liquid. However, experiments and molecular dynamics simulations indicate that this is not the case. In this paper we show how flow over a solid substrate with variations of wettability can be described in a continuum framework using the interface formation theory developed earlier. Results demonstrate that a shear flow over a perfectly flat solid surface is disturbed by a change in its wettability, i.e., by a change in the chemistry of the solid substrate. The magnitude of the effect is shown to be proportional to cos theta1 - cos theta2, where theta1 and theta2, are the equilibrium contact angles that a liquid-gas free surface would form with the two chemically different parts of the solid surface.