The rose petal effect and the role of advancing water contact angles for drop confinement

We studied the role of advancing water contact angles on superhydrophobic surfaces that exhibited strong pinning effects as known in nature from rose petals. Textured surfaces were engineered in silicon by lithographical techniques. The textures were comprised of hexagonal microstructures superimposed with randomly distributed nanospikes and were coated with a hydrophobic fluorocarbon agent. A step in the advancing water contact angle bounding specific areas was obtained by engineering a corresponding topographic step in the hexagonal micro-texture. This enabled a surface texture design confining drops to areas with a lower advancing contact angle.