Influence of topography on plasma treated titanium surface wettability

With the aim of studying the topographic influence on wettability of plasma-treated surfaces, we used eighteen commercially pure titanium (CP Titanium) disks (grade II), 10 mm in diameter and 1 mm thick, and in atmospheres of Argon (Ar), Hydrogen H2 and Ar–H2. These samples were submitted to plasma produced by hollow cathode discharge (HCD) for 20 and 60 min at a voltage of 500 V and pressure of 220 Pa. After pre-treatment, the state of the sample surfaces was assessed for surface phases with grazing incidence X-ray diffraction (GIXRD), and XPS (X-ray photoelectron spectroscopy), evaluated by atomic force microscopy (AFM) and wettability, using the sessile drop test. It was found that all the conditions were effective in reducing oxide, resulting in different wettability values. Correlation between average roughness (Ra) parameters and the ratio between maximum peak height and average distance between the highest peak and lowest valley (Rp/Rz) and wettability for the different treatment conditions were analyzed. Given the results obtained, it was concluded that Ra and Rp/Rz are not appropriate for correlating with wettability and it is suggested that a new topographic parameter be adopted for the Cassie–Baxter equation. XPS analysis showed that reduction efficacy was greater for the Ar–H2 mixture, followed by Ar and H2.