On the superhydrophobic properties of nickel nanocarpets

A surface formed by dense, aligned nickel nanowires (a "nanocarpet") was prepared by electrodeposition through an alumina membrane template, followed by dissolution of the membrane. The nickel nanowires forming the nanocarpet have a very high aspect ratio ( approximately 250), with a diameter of 200 nm and a length of several tens of micrometers. The nickel nanowires are highly rigid, perpendicularly aligned in the nanocarpet with respect to the substrate, and they touch each other at the tips, forming microscale "tepee"-shaped aggregates. By comparison, nanocarpets made of platinum nanowires have a more disordered, wave-like appearance. The nickel nanocarpet, once coated with a hydrophobic surfactant (stearic acid) has superhydrophobic properties (advancing contact angle approximately 158 degrees), and retains its superhydrophobicity after periods of immersion in water, similar to the hydrophobised platinum nanocarpet (advancing contact angle approximately 162 degrees). Interestingly, we observe that simple electrodeposition of platinum also produces pronounced superhydrophobic properties on "flat" copper surfaces. The magnetic properties of nickel might widen the range of applications in which nanocarpets can be gainfully used, such as in surfaces of switchable wettability for microfluidic applications.