Simulations of contact-line motion: Slip and the dynamic contact angle

Molecular-dynamics simulations of two immiscible fluids confined between solid walls and sheared in a Couette geometry were performed as a function of shear rate for a range of wall and fluid properties. Changes with capillary number in the interface shape and dynamic contact angle were consistent with previous analytic results. Computed velocity fields showed that the usual no-slip boundary condition broke down within 2 atomic spacings from the contact line. The slip appears to be associated with the breakdown of local hydrodynamic theory at atomic scales.