Quantitative power spectral density analysis of nano/microstructured Ni-Zn electrodeposit and its correlation with superhydrophobicity

Abstract

This paper aims to establish a quantitative relationship between wettability and surface morphology. The wettability of surfaces is highly dependent on surface morphology, and this relationship will be explored using either conventional roughness parameters or power spectral density (PSD) derived parameters. To investigate the effect of surface morphology on wettability, various Ni-Zn coatings with different hierarchical surface morphologies were electrodeposited on copper substrates. The coatings exhibited hydrophobic behavior with apparent contact angles ranging from 105° to 155°, depending on the shape, size, and arrangement of their surface features. Although conventional roughness parameters like Sq and Spc influenced the wettability of the coatings, their absolute values could not accurately predict superhydrophobic behavior. Therefore, the PSD analysis was used as an alternative approach to predict the wettability behavior of the coatings by distinguishing between nano- and micro-features. The results revealed that a superhydrophobicity (SH) index could be obtained from the PSD model to predict superhydrophobic properties. Coatings with an SH index below 0.32 exhibited a contact angle greater than 150°, regardless of their deposition parameters. The findings suggest that surface roughness plays a significant role in controlling the wettability of Ni-Zn coatings, and the SH index is a useful tool for predicting the superhydrophobic properties of these coatings.