All-solution processed, scalable superhydrophobic coatings on stainless steel surfaces based on functionalized discrete titania nanotubes

Stainless steel structures are used in reactor vessels, pipelines, boilers and industrial tubing in the oil and gas industries and they regularly experience corrosion, erosion and fouling that necessitate frequent replacement and repairs. We demonstrate a new method to robustly protect the stainless steel surface and render it superhydrophobic. Our method utilizes self-assembled monolayers (SAMs) of octadecylphosphonic acid (ODPA) grown on discrete TiO2 nanotube (d-TNT)-coated stainless steel surfaces for complete passivation. While the formation of superhydrophobic coatings based on anodically formed titania nanotube arrays has been previously reported by several research groups including us, the key techno-economic obstacle has been the need to use vacuum deposition to grow adherent and uniform precursor Ti films on non-native substrates such as stainless steel prior to electrochemical anodization. Vacuum deposition of the precursor Ti films is simply neither scalable nor economically feasible for the large and complex stainless steel structures used in pipelines, boilers and industrial tubing and solution processing, preferably a spray-coatable solution, is an absolute must. Our innovation here consists of formulating a spray-coatable suspension of functionalized discrete TiO2 nanotubes that forms a superhydrophobic surface on stainless steel substrates. Vacuum deposition is completely eliminated from our process sequence and as such, we expect our coatings to inhabit the same niche as current commercial formulations while possessing the superior temperature stability and wear resistance of TiO2.