New insight into island-like structure driven from hydroxyl groups for high-performance superhydrophobic surfaces

Abstract Island-like structure induced by hydroxyl groups has been demonstrated to pose significant influence on tuning surface morphology and wettability. Herein, with an intention to better understand this structural transformation, hydroxyl groups both from nanoparticles and substrates were controlled during the thermally-driven deposition procedure. The results show that hydroxyl groups originated from nanoparticles facilitate the fabrication of island-like structure, while these groups from substrates confine. Representatively, hydroxyl-rich TiO2 nanoparticles prefer to generate island-structure and lead to a higher water contact angle, yet hydroxyl-poor copper substrates enable the fabrication of such structure. Morphology observation convinces that nanoparticles abounded with hydroxyl groups were preliminarily grown into larger-size clusters in starting emulsion due to strong intermolecular forces, which contributes to the structural transformation from incompact layer-like to island-like. Meanwhile, the hydroxyl groups in substrates promote the uniform distribution of nanoparticles due to strong hydrogen bonding, which results in a dense and continuous layer-like surface structure. As the island-like structure improves the superhydrophobicity and bonding strength between interfaces, the surfaces with this morphology present high performances. Differing from previous findings, this work will open a new insight into the transformation of island-like structure driven by hydroxyl groups, and afford an alternative strategy to optimize the design of high-performance superhydrophobic surfaces.