Controllable wettability tuning of the stainless steel surface through successive ionic layer deposition of Zn-Fe layered double hydroxysulfate

Abstract

An efficient and scalable technique was proposed to control the wettability of stainless steel through successive ionic layer deposition (SILD) of ZnFe layered double hydroxysulfate (LDHS). The composition, structure, and surface characteristics of the coatings were investigated by EDS, XRD, SEM, Raman spectroscopy, and contact angle (CA) analysis. It was found that the coatings consisted of 2D nanocrystals with a thickness of 5–17 nm and a planar size of 55–416 nm, depending on the number of SILD cycles (n = 1–15). It was shown that their growth was accompanied by substrate-relative orientation change: 2D nanocrystals oriented horizontally at n = 1–2 and vertically at n = 3–15. The vertical orientation occurs due to the positive charge of substrate and nanocrystals surface during the SILD which results in their electrostatic repulsion. The SILD modification also leads to a change in surface wettability from weakly hydrophobic (n = 2, CA = 64.7 ± 0.6°) to superhydrophilic (n = 15, CA = 9.2 ± 0.3°). It correlates with established nanocrystals orientation since hydrophilic sulfate groups became more accessible for interaction with water in case of vertical orientation and practically inaccessible for horizontally directed nanocrystals.