Tuning wettability and getting superhydrophobic surface by controlling surface roughness with well-designed microstructures

We proposed a method to tune the wettability of a solid surface by changing its roughness. With specific designed micro square pillar arrays, the apparent contact angle of a hydrophobic surface can be continuously adjusted from the intrinsic contact angle. The samples were fabricated by combining silicon micromachining and self-assembled monolayer modification. The experimental results were closer to Cassie's theoretical predictions on the superhydrophobic surfaces than that by Wenzel's. The apparent contact angle (CA) can be tuned from the intrinsic CA to a superhydrophobic CA. The largest apparent CA in our experiments can be up to 162°, with pillars of 9.45 μm × 9.45 μm × 16 μm (width × width × height), and the spacing of 26.34 μm. By controlling the size and layout of the square micropillars, we also formed a surface with a certain roughness gradient, on which spontaneous movement of a droplet has been observed.