Electrochemical fabrication of transparent nickel hydroxide nanostructures with tunable superhydrophobicity/superhydrophilicity for 2D microchannels application

In order to survive in the harsh environments, natural creatures evolve unique wettability properties, for example, lotus leaf exhibits extreme water-repellency and Namib Desert beetle displays high wetting contrast patterns. Inspired by these natural creatures, a multifunctional surface which owns superhydrophobicity, widely tunable wettability (i.e. between superhydrophilic and superhydrophobic) and non-degraded transparency is developed. A facile and cost-effective approach via stepwise electrodeposition of nanosponge-like nickel hydroxide with the aid of self-assembled monolayers (SAMs) of non-fluorinated silane is introduced to well manipulate the pore size and surface energy. The exposed hydroxide ligands of nickel hydroxide films enhance water penetration and SAMs adsorption and thereby achieve tunable wettability from superhydrophilic to superhydrophobic. Meanwhile, the nanoscale roughness and sub-wavelength pore size of the films help maintain their optical transparency. The effectiveness of these achieved functions is demonstrated on the transparent 2D microfluidic channel fabricated by a simple electrochemical attach-detach patterning technique, which shows a fast flow speed of 5 mm s(-1) because of the strong capillary force.