Adhesion Mechanism of Water Droplets on Hierarchically Rough Superhydrophobic Rose Petal Surface

Figure 4

Microscope images of rose petal surfaces. Optical microscope images from above and side of the plump (a, b) and shrunken (c, d) nubs of the fresh and dried petals, respectively. Base diameter of the nubs is typically 20–30 μm. Round top area of the plump nubs, which is expected to contact with water droplets, is around 10 μm in diameter. Top area of the shrunken nubs is significantly smaller in comparison with the plump nubs, and thus the air gaps between the shrunken nubs are larger. Scanning electron microscope images of the dried petal surface (e, f) show that the grooved fine structure exists only on top of the nubs, not at the areas between them. The shrunken nubs possess sharp heads (f), on which a water droplet sits in a spherical shape (g) with small liquid-solid contact area.