Molecular Dynamics Study on the Dependence of Contact Angle on the Speed of Contact Line

The flow in the vicinity of a moving contact line is characterized by a steep increase in the fluid slipping relative to the solid surface owing to fluid stress concentration at the contact line. In this study, molecular dynamics (MD) simulations are made to investigate the dependence of microscopic configuration of the fluid-fluid interface, in particular the contact angle, on the speed of contact line relative to the solid surface ΔV. While ΔV increases when the solid surface velocity relative to the bulk fluid, V, is increased from zero, ΔV starts decreasing when V exceeds a certain upper limit for the given material combinations. The contact angle dependence on ΔV (and V) was predicted from the microscopic stress balance near the contact line using the fluid distribution obtained from the continuum hydrodynamic theory. It is also shown that the stress balance prediction agrees with the MD results when appropriate slip velocities are assumed in the hydrodynamic calculation.