Thermal Oxidation Fabricated Copper Oxide Nanotip Arrays with Tunable Wettability and Robust Stability: Implications for Microfluidic Devices and Oil/Water Separation

Abstract

Materials with different wettability features have attracted intensive attention due to their outstanding performances and the broad application prospects. In this work, we report an applicable and economical surface thermal oxidation method for fabricating copper oxide nanotip arrays with tunable wettability: superhydrophobicity of Cu2O nanotip array (Cu2O NA) and superhydrophilicity of CuO nanotip array (CuO NA). The superhydrophobic Cu2O NA surface presented a high water contact angle (WCA) of 161.1° and ultralow water sliding angle nearly 0°, which is an applicable property for droplet transportation in microfluidic devices. Meanwhile, the CuO NA surface exhibited a near 0° WCA as well as ultrashort wetting time for water, which indicates that the CuO NA is a promising material for oil/water separation. The dramatically transformed wettability of the two surfaces is contributed by the synergetic effect of the special convex hierarchical micro–nano structure and the nature of surface materials. The superior water affinity of CuO is attributed by the hydrolysis process, which was demonstrated by the density functional theory simulation. In addition, The Cu2O NA presented outstanding chemical and mechanical enduring reliability under harsh environments. The cost-effective fabricating process, easily controlled wettability, and special wetting performance make the Cu oxide nanotip arrays promising materials for microfluid devices and oil/water separation.