Hydrophobicity and Leidenfrost point of ZnO nanorod array combined with nanoscale roughness on the topmost surface

Abstract

Zinc oxide nanorods (ZnO-NR) were prepared using hydrothermal processing on a Si substrate. The rod diameter depended on the precursor solution concentration. Subsequent hydrothermal treatment using 3-dimethylaminopropylamine under appropriate conditions provided nanoscale roughness onto {0001}, the topmost surface of the ZnO-NR. After coating with hydrophobic fluoroalkylsilane, the ZnO-NR with the roughness on its topmost surface exhibited higher contact angles and sliding angles than the normal ZnO-NR, suggesting the contribution of Wenzel mode from the provided roughness and resultant petal surface formation. The Leidenfrost point against water droplets for normal ZnO-NR exhibited a decreasing trend concomitantly with an increasing contact angle. However, it was found to depend on the solid–liquid contact area ratio. Providing nanoscale roughness on the topmost surface of ZnO-NR decreased the Leidenfrost point.