Wetting and Active Dewetting Processes of Hierarchically Constructed Superhydrophobic Surfaces Fully Immersed in Water

When a superhydrophobic (SHPo) surface is fully submerged underwater, the surface becomes wet eventually and cannot recover the SHPo state naturally. In this paper, we fabricate hydrophobic microposts on a hydrophobic nanostructured substrate, i.e., hierarchically structured SHPo surfaces, and investigate their wetting and dewetting processes while immersed in water. All the micropost surfaces get wet, with the conditions of the water only affecting the speed of wetting. All the nanopost surfaces get wet over time after all the microposts on them are wetted. We demonstrate various active means (saturating air in water, bridging the surface to the outside air, and gas generation on the substrate) that can dewet the already wetted microposts as far as the substrate nanoposts remained nonwet. In particular, the SHPo surfaces with the recently developed electrolytic recovery mechanism are shown to maintain an SHPo state even under previously irreconcilable conditions, such as surface defects and high liquid pressure, indefinitely.