Surface modification of PTFE using an atmospheric pressure plasma jet in argon and argon + CO2

Polytetrafluoroethylene (PTFE) has many successful engineering applications due to its great chemical stability. However, for some industrial applications, the poor adhesion of PTFE to other materials is a disadvantage. To extend the PTFE application range, several methods have been developed to modify its surface properties. Among these different techniques, plasma surface modification is the most promising one and therefore, an atmospheric pressure plasma jet (APPJ) will be used in this work to modify PTFE samples. Two different discharge gasses have been used: pure argon and an argon/CO2 mixture and both plasma jets have been examined with optical emission spectroscopy to identify the plasma species present in the discharge. From these results, it was found that the discharge in argon contains argon atoms, nitrogen molecules and metastables, atomic oxygen and OH radicals, while the argon/CO2 discharge contains also radicals containing CO groups. In a second part of the work, the chemical and physical changes induced by both discharges on PTFE surfaces have been investigated using contact angle measurements, SEM, AFM and XPS. From these results, it was found that exposure times below 20 s lead to a small contact angle decrease due to the introduction of a small amount of oxygen. In contrast, at higher treatment times, the contact angle starts to increase again due to advanced chain scissions leading to a high amount of oligomeric segments on the PTFE surface. As a result of these surface degradation processes, the wettability of PTFE could not be greatly enhanced, however, in the near future, it will be investigated whether these degradation reactions can be eliminated.