Surface modification of polytetrafluoroethylene by microwave plasma treatment of H2O/Ar mixture at low pressure

Polytetrafluoroethylene (PTFE) films were treated by non-equilibrium microwave plasma of a mixture of water vapor and argon at low pressure. The properties of the PTFE surface were evaluated by means of contact angle measurements, adhesion strength measurements, attenuated total reflectance infrared spectrometry (ATR IR), and X-ray photoelectron spectrometry (XPS). The influence of some plasma parameters, such as microwave power and treatment time, has been studied. H2O/Ar plasma treatment led to a significant decrease of the water contact angle from 110.0° to 23.6° under the optimal condition, which resulted from the substantial surface defluoration and the introduction of an unusual amount of oxygen and polar functions as revealed by XPS and ATR IR spectra. When the treated samples were kept in air at room temperature, the contact angles increased markedly within a few days probably due to the evolution of chemical composition and structure of the treated PTFE surface during storage. Nevertheless, after the contact angle had reached a constant value of 60°, the plasma-treated PTFE still exhibited significantly improved wettability. Adhesion strength was improved from 26.7 to 583 N cm−2, a factor of 22, after plasma treatments.