Superhydrophilic-underwater superoleophobic NiO nanostructured surfaces: Assessment of PVP concentration effect

In this research, superhydrophilic-underwater superoleophobic NiO and nickel oxalate micro/nano structured thin films on the stainless steel (SS) meshes have been fabricated via chemical bath deposition (CBD) as a facile route. Taguchi L16 experimental design was used for optimization the effects of six important influential parameters affecting the surface wettability including molar ratio of alkaline to metallic precursor salt, alkaline agent type, NiO seed layer solution concentration, seed layer type, Polyvinylpyrrolidone (PVP) concentration and precursor type. Effect of the PVP concentration (as additive) on the oil contact angle was evaluated for the first time. The molar ratio of the alkaline to metallic salt and PVP concentration were the two most important factors having the highest impact on the underwater oil repellency behavior. The sample prepared under the optimum conditions exhibited underwater superoleophobicity with the oil contact angle (OCA) of 156.15 ± 7.5° and oil contact angle hysteresis (OCAH) of 4.3°. The X-ray diffraction (XRD) analysis, Fourier-transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FE-SEM), and roughness measurements were applied for characterization of the fabricated samples. Based on the FESEM analysis, the spherical nano- ZnO seeds have diameters of ~30–50 nm. In addition, the abrasion test was accomplished (12 cycles under 4.7kPa). The obtained results showed an excellent mechanical robustness. Moreover, an acceptable chemical durability (after 240 h) in acidic and alkaline environments with pH values of 4, 6 and 12 was observed.