Investigation On The Time-dependent Hydrophilicity In A Nano-textured Stainless Steel SUS316 Coating

Jhen-De You¹, Pei-Min Chuang¹, Pak-Man Yiu^1,2*

¹Materials Engineering, Ming Chi University of Technology, New Taipei City, Taiwan
²Center for Plasma and Thin Film Technologies, Ming Chi University of Technology, New Taipei City, Taiwan

* Presenter:Pak-Man Yiu, email:pmyiu@mail.mcut.edu.tw

While superhydrophobic surfaces demonstrate excellent stability, superhydrophilic surfaces, characterized by high surface free energy, are prone to aging effects, which degrade their wettability over time especially for metallic surfaces. Various process have been developed to impede the hydrophilic-to-hydrophobic transition upon atmospheric exposure. Limited research looked into the reason behind, thus long-term stability on the hydrophilicity of a textured surface remained a challenge. In this work we prepared a highly textured SUS316 coating by magnetron sputtering that shows superior hytrophilicity, with contact angle as small as 5°. However, it was found that upon contact with the atmosphere, contact angle increased drastically over time and eventually turned the surface hydrophobic in 30 days. We attempted to study this hydrophilic-to-hydrophobic transition phenomena by probing the aged surface with XPS and Tof-SIMS. Through XPS we found that the aged samples showed a relatively high carbon content, as well as higher C–O–C/C–C(H) ratio both on the surface and with 5s of Ar⁺ etching. Cation carbon fragments observed in TOF-SIMS spectrum further confirmed the presence of long-chain organic compounds on the aged surface. In summary, we had confirmed abundant existence of carbonaceous adsorbed layer which may account for such contrary observation.

Keywords: wettability, hydrophilicity, surface texture