Fluid epitaxialization effect on velocity dependence of dynamic contact angle in molecular scale.

Molecular dynamics simulations were used to investigate the effect of epitaxial ordering of the fluid molecules on the microscopic dynamic contact angle. The simulations were performed in a Couette-flow-like geometry where two immiscible fluids were confined between two parallel walls moving in opposite directions. The extent of ordering was varied by changing the number density of the wall particles. As the ordering becomes more evident, the change in the dynamic contact angle tends to be more sensitive to the increase in the relative velocity of the contact line to the wall. Stress components around the contact line is evaluated in order to examine the stress balance among the hydrodynamic stresses (viscous stress and pressure), the deviation of Young's stress from the static equilibrium condition, and the fluid-wall shear stress induced by the relative motion between them. It is shown that the magnitude of the shear stress on the fluid-wall surface is the primary contribution to the sensitivity of the dynamic contact angle and that the sensitivity is intensified by the fluid ordering near the wall surface.