Comparative study between in-plasma and post-plasma chemical processes occurring at the surface of UHMWPE subjected to medium pressure Ar and N2 plasma activation
- Authors
- Publication Date
- Jan 01, 2020
- Source
- Apollo - University of Cambridge Repository
- Keywords
- Language
- English
- License
- Unknown
- External links
Abstract
Surface chemical properties triggered by plasma activation of polymers were extensively investigated. However, clear distinctions between particular mechanisms occurring in-plasma and post-plasma treatment performed at medium pressure are up-to-the-minute missing and are therefore constituting the study aim. Polyethylene films were subjected to N-2 and Ar plasma using a dielectric barrier discharge operating at 5.0 kPa with a minimally oxygen-contaminated chamber. A distinctive combination of optical emission spectroscopy and in-situ X-ray photoelectron spectroscopy (XPS) was used to characterize in-plasma species/surface interactions. Post-plasma oxidation was unraveled by exposing plasma-treated samples to ambient air and performing ex-situ XPS. In-situ XPS showed remarkably high nitrogen (20.6%) with negligible oxygen incorporation (2.8%) thus exceptionally enhancing N-selectivity when comparing to the state-of-the-art. More oxygen (5.9%) was however detected after Ar activation due to high energy metastables dissociating O-2 impurities. Upon exposure to ambient air, post-plasma oxidation occurred producing more oxygen mainly in the form of O-C-O and N-C-O groups on N-2-activated surfaces and C-O groups on Ar-activated surfaces. Above a certain storage time, physical processes of polymeric chain reorientation prevailed over chemical processes. Overall, in- and post-plasma surface interactions were discriminated in this work that constitutes a perfect-picture reference for polymer plasma activation.
