Easy Route to the Wettability Cycling of Copper Surface between Superhydrophobicity and Superhydrophilicity

A hierarchical copper structure combining micro- and nanogaps/pores was built up on copper substrate by etching and electrodeposition. The fresh as-deposited copper was easily oxidized in air at room temperature, forming a CuO layer covering on the surface. The surface could be hydrophobized with thiol-modified fluorocarbons, after which it showed a water contact angle as high as 165 degrees +/- 2 degrees. This surface could also regain the superhydrophilicity with a zero water contact angel after annealing at 200 degrees C for 10 min to desorb the low surface energy monolayer of thiol-modified fluorocarbons and reform a CuO layer again on the surface. Repeating the process of adsorption/desorption of the monolayer by modification and annealing, it was successful to fulfill the wettability cycling between superhydrophobicity and superhydrophilicity on the copper surface. The adsorption and desorption mechanism of the monolayer was discussed based on the result of surface chemistry analysis.