  Three-dimensional hierarchical ZnO films with lotus-leaf-like micro/nano
structures were successfully fabricated via a biomimetic route combining
sol-gel technique, soft lithography and hydrothermal treatments. PDMS mold
replicated from a fresh lotus leaf was used to imprint microscale pillar
structures directly into a ZnO sol film. Hierarchical ZnO micro/nano structures
were subsequently fabricated by a low-temperature hydrothermal growth of
secondary ZnO nanorod arrays on the micro-structured ZnO film. The morphology
and size of ZnO hierarchical micro/nano structures can be easily controlled by
adjusting the hydrothermal reaction time. Wettability of hierarchical ZnO thin
films was found to convert from superhydrophilicity to hydrophobicity after a
low-surface-energy fluoroalkylsilane modification. Improved wetting properties
from hydrophobic to superhydrophobic can be tuned by increasing the growth of
ZnO nanorods structures.
