Modification of PET surface properties using extremely non-equilibrium oxygen plasma

Polyethylene terephthalate (PET) foils have been exposed to oxygen plasma and its afterglow in order to reveal compositional and structural modifications of the surface layer. Oxygen plasma was created by electrodeless RF discharge in a glass chamber so the O-atom density was close to 10(22) m(-3) although the density of charged particles was only about 1 x 10(16) m(-3). Long-living reactive particles created in plasma were leaked into the afterglow chamber using a two-stage rotary pump of pumping speed 4.4 x 10(-3) m(3) s(-1). The density of O-atoms in the afterglow as measured with a catalytic probe was 3 x 10(21) m(-3), while the density of reactive oxygen molecules was estimated theoretically. The functionalization was accomplished even after a brief exposure to either plasma or afterglow since all samples were saturated with oxygen-rich functional groups as revealed by XPS. The water contact angle measurements, however, showed that only plasma treatment allowed for super-hydrophilicity, explained by rich surface morphology as detected by AFM. The differences in morphological properties between plasma and afterglow treated samples were explained by different interaction mechanisms between low and high energy particles impinging the polymer surface.