Etching Processes of Polytetrafluoroethylene Surfaces Exposed to He and He-O2 Atmospheric Post-discharges

TL;DR

This study compares the effects of helium and helium-oxygen atmospheric plasmas on PTFE surfaces, revealing physical etching mechanisms and changes in surface properties like roughness and hydrophobicity.

Contribution

It provides new insights into the surface modification mechanisms of PTFE by atmospheric plasmas, highlighting the role of helium metastables and oxygen in etching and surface property changes.

Findings

Pure He plasma causes physical etching without surface chemistry change.

He-O2 plasma reduces etching species and increases surface roughness.

Oxygen atoms preferentially etch the amorphous phase, creating alveolar structures.

Abstract

A comparative study of polytetrafluoroethylene (PTFE) surfaces treated by the post-discharge of He and He-O2 plasmas at atmospheric pressure is presented. The characterization of treated PTFE surfaces and the species involved in the surface modification are related. In pure He plasmas, no significant change of the surface has been observed by X-ray photoelectron spectroscopy (XPS), dynamic water contact angles (dWCA) and atomic force microscopy (AFM), in spite of important mass losses recorded. According to these observations, a layer-by-layer physical etching without any preferential orientation is proposed, where the highly energetic helium metastables are the main species responsible for the scission of --(CF2)n-- chains. In He--O 2 plasmas, as the density of helium metastables decreases as a function of the oxygen flow rate, the treatment leads to fewer species ejected from the PTFE surfaces (in agreement with mass loss measurements and the detection of fluorinated species onto aluminum foil). However, the dWCA and AFM measurements show an increase in the hydrophobicity and the roughness of the surface. The observed alveolar structures are assumed to be caused by an anisotropic etching where the oxygen atoms etch mainly the amorphous phase.