Surface analysis of poly(ethylene naphthalate) (PEN) films treated at atmospheric pressure using diffuse coplanar surface barrier discharge in air and in nitrogen

Abstract

Surface modification of poly(ethylene naphthalate) (PEN) films by Diffuse Coplanar Surface Barrier Discharge (DCSBD) in ambient air and nitrogen at atmospheric pressure was studied at short plasma exposure times from 1 s up to 10 s. Chemical changes in the surface composition after the plasma treatments were studied using a high resolution XPS (X-ray Photoelectron Spectroscopy). The water contact angle was reduced from an initial value of 79° to values of 31° and 20° for the ambient air and nitrogen plasma treatments. After 3 days of storage in ambient air the contact angles were still about 50° and 40°, respectively. The polar component of surface energy was changed by the aging significantly less than the total surface energy. Despite the marked increase in the surface energy, the plasma treatment had no significant influence on the surface morphology.The surface modification in air plasma resulted in significant reduction the OC bond formation on the treated surface. The concentration of oxygen on PEN surface was increased from an initial value of 22 at.% up to 45 at.% already after 5 s air plasma exposure, and this oxygen concentration remained constant for longer plasma treatments. A small presence of nitrogen under 1.5 at.% from the air was also found after the treatments. The nitrogen plasma modified surface composition only by implanted nitrogen up to 5 at.% when the ratio of CO and C–O was not significantly changed. But some new bonds are also expected to be formed in a very low number only.