Antithetic superhydrophobic/superhydrophilic surfaces formation by simple gas switching in an atmospheric-pressure cold plasma treatment

The wettability control of surfaces is a significant issue in many industrial fields such as encapsulation, water repellency enhancement, oil recovery, etc. From a practical point of view, to reach the intended surface wettability, it is important for a surface modification process to be low-cost, easily implemented and fast. Therefore, in this work, a facile plasma deposition method is suggested to form surfaces with antithetic wettabilities, i.e. superhydrophobic and superhydrophilic, via simple introduction of additive gases in an atmospheric-pressure plasma generated with argon and hexamethyldisilazane (HMDS). The hydrophobic surface (WCA: 115°) modified by Ar/HMDS plasma is easily switched to superhydrophobic surface (WCA: 160°) by N₂ addition and to superhydrophilic surface (WCA: 10°) by O₂ addition. From physical and chemical analyses of plasma treated surfaces, a small amount of N₂ or O₂ gas is shown to dramatically change the surface morphology and chemical composition. Besides, by finely tuning the additive gases flow rates, the surface wettability could be continuously modulated in the whole ∼0° to 160° water contact angle range.