Abstract
Microscopic contact angle on a moving contact line traveling over a step with a height of 0.3〜1.2 nm is investigated with molecular dynamics simulation. The simulations were made with a Couette flow geometry where two immiscible fluids are sheared between two parallel plates, one of which is equipped with step-structured surface. The contact lines strongly tend to be captured (pinned) at the edge of the convex step and the minimum contact angle observed at the moment of the depinning of the contact line is dependent on the height of the steps. An analytical model for the estimation of the relation between the minimum contact angle and the step height is developed. By taking account into the deviation between the normal and tangential components of the pressure distribution near the interface, the model reproduces well the increase of the minimum contact angle with the decrement in the step height.
