Engineering hydrophobic stainless-steel surfaces

Hydrophobic behavior has been engineered in polymers, glasses, silicon, and even some metals by utilizing a wide range of wet and dry methods to change their surface energies. Often these surface modifications require the use of toxic chemicals like fluorosilanes or require complicated multistep processing. In this work, an alternative method is presented where the surface of stainless steel is made hydrophobic without exposure to silanes or complicated surface processing. 316 L stainless steel powder was combined with carbon nanotubes (CNT) via high-energy ball milling and printed into either square plates or rectangular bars topped with a pillared array by laser powder bed fusion. Sessile drop contact angle measurements, optical profilometry, and microscopy were performed revealing most samples were hydrophilic. When the CNT loading was 3 vol%, however, hydrophobic behavior was observed. Further, a wicking effect was observed on pillared samples showing short-duration support of a water droplet for up to tens of minutes before dropping to the substrate. Trends indicate that further increasing CNT concentration, adjusting laser energy density, and/or changing model specifications could lead to increased hydrophobicity.