The CA increases slightly from 153° to 155° when the dimension of Si micropillars reduces from 16 to 8 μm (see Table  1). The mobility of water droplets on a CNT forest ISRIB supplier surface see more was investigated by measuring the SA. Figure  2c shows an image of a water droplet which begins to slide on an inclined CNTs/Si surface with a slope of approximately 50°. It shows a significant

CA hysteresis of approximately 77° with an advancing angle of Φ a = 163° and a receding angle of Φ r = 86°. The SA of CNTs/Si varies from 40° to 50° according to the height of the CNT forest (see Table  1). The large CA hysteresis implies that it is hard for water droplets to slide on the CNTs/Si surface. Figure  2d shows an optical image of a water droplet sliding on CNTs/Si-μp. The water droplet on hierarchical CNTs/Si-μp has no evident hysteresis with an ultralow SA of 3° to 5°. The ultralow

SA implies that water droplets are easy to slide on the CNTs/Si-μp surface. We further reveal the behaviors of tiny water droplets on CNTs/Si and CNTs/Si-μp. Because the SA of CNTs/Si-μp is 3° to 5°, we mounted CNT samples on an inclined substrate with a slope of 5°. The CNT forest is then exposed under tiny water droplets with a diameter of 50 to 500 μm sprayed from a nebulizer (see Figure  3a). The situations of tiny water droplets are quite different from those of large droplets used in SA measurement. selleckchem Some of the tiny droplets might join into larger ones and slide down on the CNTs/Si-μp, while some of them might stick on the CNTs/Si-μp

surface. The water droplets sticking on the CNTs/Si-μp surface have a round shape (see Figure  3b). The largest water droplets we observed on the CNTs/Si-μp surface have a diameter less than 0.8 mm (approximately 0.27 μL), which implies that water droplets larger than 0.3 μL might slide on the CNTs/Si-μp surface with a tilted angle of 5°. It indicates that the hierarchical CNTs/Si-μp can be used to collect tiny water droplets. Most of the tiny water droplets Casein kinase 1 are absorbed by the CNT forest eventually within 10 min. The CNTs/Si-μp surface is thus wetted by exposing under tiny water droplets for a long time. However, the wetted CNTs/Si-μp surface still shows superhydrophobic behaviors after it dries up. Figure  3c shows an image of the CNTs/Si-μp exposed under tiny water droplets after three time tests. The shape of water droplets is quite similar to those in Figure  3b, which indicates that the CNTs/Si-μp surface still shows hydrophobic properties after wetting using the tiny water droplets. Figure 3 Representation of water droplets in different conditions. (a) Schematic figure of tiny water droplets sprayed from a nebulizer. (b) Tiny water droplets on CNTs/Si-μp surface. (c) Water droplets on CNTs/Si-μp after three time tests. (d) Water droplets on CNTs/Si surface.