Directional migration of an impinging droplet on a surface with wettability difference

Direct numerical simulation is employed to study the behaviors of droplets impinging a surface with a wettability difference. Unlike the four stages of a droplet passing through on homogeneous surfaces, results illustrate that the droplet undergoes asymmetric spreading, retracting, detaching, and self-migrating phases when it impacts the surface with nonuniform decorations. This happens because of the unbalanced Young's force acting on the three-phase contact line around the drop periphery, which points toward the direction of increasing wettability, or decreasing contact angle.