Self-assembly of metal nanorod arrays into hierarchical clusters and evolution of their hydrophobic behaviour

Electrochemically grown copper nanorod arrays form clusters when they are dried after etching. By optimizing the aspect ratio and the drying conditions, we can tune the interplay between the two competing forces: elastic force due to bending and the surface tension from the evaporating internanorod liquid and consequently get clusters of varied sizes and shapes. Static contact angle and contact angle measurements on a tilt were done for the clusters, and it was observed that the hydrophobicity and the pinning properties of the clustered surfaces depend on three main physical parameters-rod length, single cluster size and cluster size by inter-cluster separation ratio. The clusters are double hierarchical structures where air traps in between the clusters (microstructures) determine the static contact angle and wetting of the nanorods (nanostructures) contained within each single cluster determines the pinning.