Preparation and characterization of gradient wettability surface depending on controlling Cu(OH)2 nanoribbon arrays growth on copper substrate

Gradient wettability surface was prepared on copper substrate via a facile alkali assistant surface oxidation technique. It was based on the control of cupric hydroxide (Cu(OH)2) nanoribbon arrays growth from the upper part to lower part along the vertically placed copper substrate in an aqueous solution of NaOH and (NH4)2S2O8. Thus the gradient wettability functionalized Cu(OH)2 nanoribbon arrays were directly fabricated on copper substrate by varying the immersing time of different positions along the substrate surface. By using a relative dilute NaOH solution (0.75 mol/L) and (NH4)2S2O8 solution (0.03 mol/L), and regulating dropping speed, the surface gradient wettability changing from the original contact angle of copper substrate (90.5°) to surperhydrophilicity (3.0°) was prepared. The surface fabricated on copper substrate may keep its gradient wetting property after immersed in water bath at 100 °C for 10 h. The water contact angle measurement (CA), Scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were employed to analyze the wettability, morphologies, crystal structure, and surface chemical compositions of the Cu(OH)2 nanoribbon arrays on copper substrate. This research is expected to be significant in providing a new strategy for the preparation of novel gradient wettability material with potential industrial applications on copper substrate.