Directional wetting behavior, is frequently observed in nature and is often attributed to asymmetric micro- and nanostructures on biological surfaces. Inspired by the anisotropic wetting properties of butterfly wings, we fabricated tilted micropillar and cantilever structures using MEMS technology, and evaluated their directional wetting characteristics in terms of contact angle and sliding angle. While both structures exhibited high water repellency with contact angles exceeding 140°, no significant anisotropy was observed in the contact angles themselves. In contrast, the sliding angle demonstrated clear anisotropic behavior: for tilted pillar structures, the sliding angle was smaller in the direction of the tilt compared to the opposite direction. For the cantilever structures, directional differences were observed between the tip-to-base and base-to-tip directions, as well as between directions parallel and perpendicular to the beam axis.
Kenji SUZUKI (Wed,) studied this question.