Effect on surface wettability of GLAD synthesized annealed NiO nanowire

Abstract

The wettability of a surface contributes a significant role in fluid interaction, and it can be controlled or altered to achieve the desired surface wettability. The conventional way of altering surface wettability, like coatings and chemical treatment methods has been replaced by annealing in this approach without involving any modification of the structure. In this paper, nickel oxide (NiO) nanowires (NWs) were fabricated by the glancing angle deposition (GLAD) technique, which is a catalyst-free deposition technique. The structure and morphology of the fabricated NWs were confirmed by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), and transmission electron microscope (TEM) analysis. The annealing process altered the wettability behavior of the as-deposited NW surface from a hydrophobic to hydrophilic nature. From an atomic force microscope (AFM) image, the wettability of both sample’s surfaces was induced with the root means square roughness (R_r.m.s) and mean roughness (R_a), which were 10.42 nm, and 8.26 nm for as-deposited, whereas 2.26 nm and 1.78 nm for annealed sample, respectively. In addition, contact angle measurement also revealed the wettability nature of the surface and its influence on dynamic water droplets, which was investigated using surface inclination, and the extraction-contraction method. The sliding angle increases from 19° to 42° with the increase in frictional force and adhesion of the surface from 6.38 μN to 13.11 μN and from 24.56 mN/m to 115.33 mN/m, respectively. Overall, the obtained surface wettability was tuned based on external stimuli to demonstrate a practical application for self-cleaning, oil–water separation, agricultural water harvest systems, and bioscience applications.