Design and understanding of superhydrophobic ZnO nanorod arrays with controllable water adhesion

How to understand and facilely design superhydrophobic surfaces with controllable water adhesion has aroused increasing interest because of their promising applications such as self-cleaning, heat transfer, and oil/water separation. In this study, we report the design and fabrication of superhydrophobic ZnO nanorod arrays with controllable water adhesion by coating environmentally-friendly Cu2O nanoparticles. Besides the lower surface free energy of Cu2O than that of ZnO, the formation of the hierarchical micro-nanostructures consisting of ZnO nanorod arrays and Cu2O nanoparticles is propitious to decrease the contact area between water droplets and material surfaces. As a result, as-induced weak van der Waals force prompts the low water adhesion of superhydrophobic surfaces. In contrast, to obtain a higher adhesive surface it is necessary to design the microstructures making the van der Waals force enhancing by increasing the contact area or making the capillary adhesive force appearing by sealing fraction of air in the interfacial microgrooves. These results are interesting and significant to further understand and manipulate liquid collection/transfer by controlling the liquid adhesion on solid surfaces.