Polyethylene terephthalate surface modification by filamentary and homogeneous dielectric barrier discharges in air

In this paper, polyethylene terephthalate (PET) films are modified using nonequilibrium plasma generated by homogeneous dielectric barrier discharges (DBDs) in air at medium pressure, and the results are compared to those treated by using filamentary DBDs in air at atmospheric pressure. The characteristics of homogeneous DBDs are studied and compared with those of filamentary DBDs by measuring their electrical discharge parameters and observing their light-emission phenomena, and the surface properties of PET films before and after the treatments are studied using contact-angle and surface-energy measurements, X-ray photoelectron spectroscopy, and scanning electron microscopy. It is found that the homogeneous DBD is quite homogeneous and stable in the whole gas gap, which differs from the filamentary DBD, and the plasma treatments modify the PET surface in both morphology and composition. The PET films modified in both treatments show a remarkable decrease in water contact and a remarkable increase in surface energy due to both the introduction of oxygen-containing polar groups onto the surface and the improvement in surface roughness. It is found that the homogeneous DBD is more effective in PET surface modification than the filamentary DBD as it can make the contact angle decline to a lower level by introducing more oxygen-containing groups, and the possible reason for this effect is discussed.