Figure 2. SEM images of the untreated stainless steel mesh and measured water contact angle.

Stainless steel meshes (316 L) with 150 μm pore size and 100 μm mesh wire thickness were used because of their high mechanical strength, durability and commercial availability. Meshes were purchased from Sigma-Aldrich. Figure 2 shows SEM images of the untreated mesh. Note that surface of wires had structures in the form of lines along wire direction and some irregularities at the positions of wires overlaps, which were resulted from the manufacturing method of wires and meshes. These structures with combination of meshes geometry could be responsible for the relatively high WCA for untreated meshes (~128^o). After preparation, the laser textured meshes were aged in ambient air for 30 days under the same conditions, with supporting constant temperature and humidity (21.5^o C and 45% humidity).

Firstly, we describe the process of samples preparation using different gases. Mesh samples were structured inside Chamber #1. The air at 1 atm was purged inside the chamber for laser treatment of meshes at ambient conditions. In the case of different gases the procedure was as follows. Initially we pumped the chamber with meshes down to the vacuum conditions of 2×10^-4 mbar. Then the sample was stored at these conditions for 30 min allowing additional cleaning and gas removal from the sample’s surface. Then, in the case of treatment at particular gas environment, the valve between chamber and pump line was closed and the gas was inserted inside the chamber. For all gases the same pressure at about 200 mbar was used. After gas purging, the sample was textured by laser radiation. Finally, before opening chamber, the treated sample was stored for 2 hours in the same gas environment. Immediately after extracting from chamber, the sample was tested to measure WCA. In the case of laser treatment in atmospheric air or only in vacuum the same ageing time was used. Alongside with influence of the gas environment, the variation of scanning speed and polarization caused the morphology and wettability variations.