Generation of hierarchical micro-structures for anisotropic wetting by elliptical vibration cutting

This paper reports enhanced anisotropic wettability using two-level hierarchical micro-structures. First-order micro-channels with superimposed second-order micro-textures were machined on aluminum surfaces using ultrasonic elliptical vibration cutting (EVC). Controllable sinusoidal micro-textures with a wavelength one order of magnitude smaller than the widths of the first-order micro-channels were applied to the surface. Anisotropic wettability was evaluated by water contact angle measurements in two orthogonal directions. The results have shown that the generated hierarchical micro-structures have nearly doubled the anisotropic contact angle in comparison to one-level structures. A relationship between anisotropic wetting characteristics and process parameters is also presented.