Bio-inspired hierarchical hair arrays with tunable adhesive superhydrophobicity

Inspired by the hierarchical seta arrays on the feet of gecko and the legs of water strider, two different microstructures including cylindrical hair arrays and coniform hair arrays have been fabricated by reactive ion etching combined with colloidal lithography. Interestingly, all the artificial hair arrays are sculptured with elaborate nanogrooves, leading to a unique hierarchical structure. Inspired by the novel hierarchical structures, the contrastive experimental research for their wetting properties was carried out by means of optical contact angle measurement. The results show that after fluorination, both of the two hair arrays exhibit excellent superhydrophobicity, but different adhesive force towards water. These tunable adhesive superhydrophobicity may be attributed to the different morphologies of the hair arrays. Based on these properties, a "mechanical hand" to transport small water droplets from a superhydrophobic surface to a hydrophobic or a hydrophilic surface without any loss or contamination was realized.