Competitive and synergistic effects between excimer VUV radiation and O radicals on the etching mechanisms of polyethylene and fluoropolymer surfaces treated by an atmospheric He–O₂post-discharge

Abstract

Among various surface modification techniques, plasma can be used as a source for tailoring the surface properties of diverse materials. HDPE and fluoropolymer surfaces have been treated by the post-discharge of an atmospheric RF-plasma torch supplied with helium and oxygen gases. The plasma-treated surfaces were characterized by measurements of mass losses, water contact angles, x-ray photoelectron spectroscopy and atomic force microscopy. This experimental approach correlated with an optical characterization of the plasma phase allowed us to propose etching mechanisms occurring at the post-discharge/polymer interface. We discuss how competitive and synergistic effects can result from the oxidation and/or the roughening of the surface but also from the excimer VUV radiation, the He metastable species and the O radicals reaching the plasma-polymer interface.

Cold Atmospheric Pressure Plasma VUV Interactions With Surfaces: Effect of Local Gas Environment and Source Design

“…The introduction of oxygen to the feed gas of the MHz APPJ source shows less thickness loss with a MgF 2 filter in place over the sample, which corresponds to only the VUV effect (Figure ). This result matches well with previous work by Dufour who show this decreased VUV effect with molecular oxygen addition to the feedgas . Additionally, the addition of oxygen quenches the metastables that are responsible for the formation of Ar excimer and the VUV radiation.…”

“…They also show that VUV photons alone are relatively ineffective at deactivating bacteria whereas combined VUV and reactive species treatment has the largest effect. Dufour et al discusses VUV emission from a He and O 2 admixture MHz frequency plasma torch (AtomfloTM by SurfX). They propose that the mechanism for surface modification is based on a He 2 * excimer which emits at near 60 nm.…”

LDPE Surface Modifications Induced by Atmospheric Plasma Torches with Linear and Showerhead Configurations

“…The pure He flowing post‐discharge generates highly‐excited states of He, He metastables, O, and OH radicals. Although some VUV are known to be emitted by plasma, the effect of these radiations can be considered as negligible for the treatment of polymers due to the ambient air oxygen absorption . In the pure Ar post‐discharge, the main species are highly‐excited states of Ar but also OH and O radicals .…”

“…Mixing O 2 with the He carrier gas consumes the He metastable species to produce O 2 + and N 2 + ions through Penning ionization reactions but also enhances the production of O radicals and O 2 metastables . Mixing O 2 with the Ar carrier gas leads to the consumption of the Ar metastable species through reactions different from Penning ionizations of O 2 as no emission of O 2 + ions could be evidenced.…”

Molecular Surface Analysis and Depth-Profiling of Polyethylene Modified by an Atmospheric Ar-D2O Post-Discharge

“…This chemical damage can be ascribed to Ar + and Ar M arising from the plasma medium . Moreover, the VUV radiations emitted by the plasma have a negligible effect in ambient air because of the oxygen absorption . Finally, the observed N‐uptake can be explained by the grafting of N 2 molecules from the atmosphere …”