Unraveling Exclusive In-Plasma Initiated Oxidation Processes Occurring at Polymeric Surfaces upon O-2 Admixtures to Medium Pressure Ar and N-2 DBD Treatments

Polymeric surfaces have been increasingly plasma-activated to adopt adequate chemistries, enabling their use in different applications. An unavoidable surface oxygen insertion upon exposure to non-oxygen-containing plasmas was always observed and mainly attributed to in-plasma oxidation stemming from O-2 impurities in plasma reactors. Therefore, this work investigates exclusive in-plasma oxidation processes occurring on polyethylene surfaces by purposely admixing different O-2 concentrations to medium-pressure Ar and N-2 dielectric barrier discharges (base pressure: 10(-7) kPa). Hence, distinctive optical emission spectroscopy and in-situ X-ray photoelectron spectroscopy (XPS) data were carefully correlated. Pure N-2 discharge triggered an unprecedented surface incorporation of large nitrogen (29%) and low oxygen (3%) amounts. A steep rise in the O-content (10%) at the expense of nitrogen (15%) was detected upon the addition of 6.2 x 10(-3)% of O-2 to the feed gas. When the added O-2 exceeded 1%, the N content was completely quenched. Around 8% of surface oxygen was detected in Ar plasma due to high-energy Ar metastables creating more surface radicals that reacted with O-2 impurities. When adding only 6.2 x 10(-3)% of O-2 to Ar, the surface O content considerably increased to 12%. Overall, in-plasma oxidation caused by O-2 impurities can strikingly change the surface chemistry of N-2 and Ar plasma-treated polymers.