Optimization of surface wettability of polytetrafluoroethylene (PTFE) by precise dosing of oxygen atoms
Dane Lojen, Rok Zaplotnik, Gregor Primc, Miran Mozetič, Alenka Vesel
Abstract
Fluorinated polymers such as PTFE cannot be functionalized with polar, oxygen-containing functional groups by a one-step treatment with oxygen plasma because the treatment would preferentially lead to surface etching rather than substitution of fluorine with oxygen. A novel method for the functionalization of PTFE is presented. PTFE was initially treated in low-pressure non-equilibrium inductively coupled RF hydrogen plasma in the H-mode to obtain an appropriate surface finish for functionalization with oxygen atoms. The hydrogen-plasma treatment ensured the formation of a polyolefine-like surface film, which was functionalized with polar groups by subsequent exposure to a fluence of O atoms in the range between approximately 1 × 1022 m−2 and 1 × 1026 m−2. The evolutions of the surface wettability and composition were studied systematically in this range of O-atom fluences. A deep and rather broad minimum of the water contact angle (WCA) was observed. The minimum of the WCA was correlated to the concentrations of elements in the surface as analysed by X-ray photoelectron spectroscopy. A complete hydrophobic recovery was observed at the largest O-atom fluence, which coincided with the restoration of the surface composition. The surface kinetics upon exposure to O atoms or a weakly ionized oxygen plasma was studied and explained.