Understanding polyethylene surface functionalization by an atmospheric He-O$_2$ plasma through combined experiments and simulation

TL;DR

This study combines experiments and simulations to understand how atmospheric He-O2 plasma treatment modifies polyethylene surfaces, revealing the formation of oxygen-containing functional groups and their subsurface behavior.

Contribution

It provides new insights into the surface chemistry and reaction mechanisms of polyethylene during atmospheric plasma treatment through combined experimental and molecular dynamics approaches.

Findings

Surface hydrophilicity increases after plasma treatment

Oxygen functional groups form on the surface and subsurface

Simulations show oxygen atoms remain near the surface before reacting

Abstract

High density polyethylene surfaces were exposed to the atmospheric post-discharge of a radiofrequency plasma torch supplied in helium and oxygen. Dynamic water contact angle measurements were performed to evaluate changes in surface hydrophilicity and angle resolved x-ray photoelectron spectroscopy was carried out to identify the functional groups responsible for wettability changes and to study their subsurface depth profiles, up to 9 nm in depth. The reactions leading to the formation of C-O, C=O and O-C=O groups were simulated by molecular dynamics. These simulations demonstrate that impinging oxygen atoms do not react immediately upon impact but rather remain at or close to the surface before eventually reacting. The simulations also explain the release of gaseous species in the ambient environment as well as the ejection of low molecular weight oxidized materials from the surface.