Paper PS1+SE-MoM5
Streamers Effects in Cold Atmospheric Plasma Applications: Coatings, Gas Conversion, Surface Chemistries

Monday, October 21, 2019, 9:40 am, Room B131

For a long time, research in atmospheric plasma dielectric barrier discharges (DBDs) focused on homogeneous discharges. However, most of the DBDs present inhomogeneities in the form of streamers.

In this presentation, we aim at showing the drastic effect of these streamers on the chemical reactivity of the discharges. Consequences can be found for instance on the chemistry and on the roughness of plasma deposited coatings, on the deposition rates, or on the conversion of gases inside the discharge. These streamers can be studied through a high speed/high sensitivity camera, and by recording the current – voltage curves with a Rogowski coil on an oscilloscope. The chemistry in the plasma phase is studied using mass spectrometry, optical emission spectroscopy and gas chromatography. Roughness can be measured using profilometry or AFM, and the surface chemistry is analyzed by XPS.

The effect of the streamers will be demonstrated using the following examples :

- the plasma polymerization of CFx coatings, in Argon or Helium leads to different coatings chemistriess and roughnesses, induced by the streamers. This leads to coatings with contact angle varying from 110° (PTFE like) to more than 140°.

- the plasma polymerization of anhydrides shows that the number of streamers depends on the nature of the anhydride injected, and more specifically on the presence of double bonds, and their location. This affects the final chemistry of the coatings, but also the deposition rate.

- the conversion of CO₂ by a DBD is a highly filamentary discharge. Although this is due to the electronegative nature of CO₂, we show that, by changing the dielectric, and by playing with the plasma parameters, one can significantly vary the number of streamers. We also show that this number of streamers seems to be a key factor for the gas conversion.