| AVS 63rd International Symposium & Exhibition | |
| Plasma Science and Technology | Monday Sessions |
| Session PS+SE-MoM |
| Session: | Atmospheric Pressure Plasma Processing |
| Presenter: | Stéphanie Collette, Université Libre de Bruxelles, Belgium |
| Authors: | S. Collette, Université Libre de Bruxelles, Belgium P. Viville, Université de Mons, Belgium F. Reniers, Université Libre de Bruxelles, Belgium |
| Correspondent: | Click to Email |
In the literature, some studies focus on the use of H2O in plasma discharges because of its potential high reactivity. However, is also known to destabilize plasmas. In this study, the reactivity of water at the interface between the plasma and the surface of the low density polyethylene (LDPE) was investigated. LDPE is chosen as polymer because of its high capacity to be functionalized.
In the first part of this project, we study the water reactivity in atmospheric plasma by injecting H2O vapor in the discharge of a dielectric barrier discharge, supplied with Ar as carrier gas. OES evidenced the production and the consumption of Ar, O, OH, and N2 species. They can be quantified as a function of the H2O flow rate and the treatment time in order to have a better understanding of the reactivity. Some chemical reactions occurring within the discharge can be highlighted. To characterize the discharge itself, current measurements are performed and a high speed camera is used to observe the changes of the discharge (number and size of the streamers).
In the second part of this research, LDPE surfaces exposed to water-containing plasma are characterized by XPS. The measurements of the O 1s peak reveal a strong increase of oxygen from 0% to 16%. XPS Depth profiles evidence the diffusion of O in the subsurface. These results have been compared with WCA measurements expressed as a function of time. Between 0 and 30 s, a strong decrease in the WCA is observed (from 100° to 63°) and can be linked to the rise of the O% (from 0% to 13%). After 30 s, the WCA rapidly decreases to 43° which seems inconsistent with the very slow increase of the O% (almost no rise) observed by XPS. In parallel, AFM measurements show a texturization of the treated LDPE, as the surface roughness increases from 27 nm to 75 nm. The effect observed after 30 s of treatment can be explained by the Wenzel equation:
Cos Θapp = r cos Θ
Indeed, the “r” factor in the Wenzel corresponds to the roughness ratio defined as the ratio of true area of the solid surface to the apparent area. Cos Θ can be linked to the polar component of the surface energy and therefore to the oxygen concentration at the surface. The roughness and the oxygen content increase simultaneously with time and the combination of these two factors lead to obtain a higher Cos Θapp. Indeed, the texturization and the grafting of oxygen are correlated by the use of the Wenzel equation thereby allow the understanding of the large decrease of WCA.
This work is supported by the Belgian Federal Government (Interuniversity Attraction Belgian Science Policy IAP research project P7/34 – Physical Chemistry of plasma surface interactions).