Surface Analysis on Wettability of Nickel Foams

Abstract

In this work, the wettability of nickel foam (NF) has been carefully examined using the x-ray photoemission spectroscopy (XPS) and water contact angle (WCA) measurements. NFs with varied wettability from hydrophobic to superhydrophilic have been prepared by various methods including chemical etching, thermal treatment and atmospheric exposure. The WCA results show that the asobtained NF is hydrophobic which can be converted to hydrophilic by either hydrochloric etching or calcining. The hydrophobic behavior can then be restored by moist air exposure. By using XPS, the strong variation of the Ni 2p3/2 and O 1s spectra has been observed and interpreted in the modified NFs with diverse wettability. Our results indicate that wetting behavior is driven by the formation and ratio of hydrophobic (i.e. Ni(OH)2 and organic overlayers), hydrophilic (Ni, NiO) and water-soluble (NiCl2) species on the NF surfaces. The change of surface morphology determined by scanning electron microscopy (SEM) is used to describe different hydrophobic recovery rates on various samples. These findings suggest that surface analysis is important to evaluate the wettability of NFs.