| AVS 56th International Symposium & Exhibition | |
| Plasma Science and Technology | Friday Sessions |
| Session PS-FrM |
| Session: | Plasma Science for Medical and Biological Applications |
| Presenter: | J. Prégent, Université de Montréal, Canada |
| Authors: | J. Prégent, Université de Montréal, Canada F. Busnel, Université Laval, Canada V. Blanchard, FPInnovations-Division Forintek, Canada L. Stafford, Université de Montréal, Canada |
| Correspondent: | Click to Email |
The use of wood products in architectural or exterior applications is often limited by the short durability of these products and the fast deterioration of their appearance. Several waterborne coatings aimed at preserving the wood properties have been developed but these coatings are often characterized by poor adhesion on wood surfaces. To improve adhesion, we investigated modification of the surface properties of wood samples following their exposition to the afterglow of an atmospheric pressure dielectric barrier discharge in N2/O2 mixtures. The surface energy divided into a dispersive (non-polar) part, γDS, and a polar part, γPS, was determined by means of contact angles measurements. For polar sugar maple samples, γPS decreased from 78.5 mJ/m2 before treatment to 59.0 mJ/m2 after N2 plasma exposure. γPS further decreased with the introduction of O2, reached a minimum value of 31.2 mJ/m2 at 85%N2-15%O2, and then increased until it reached its untreated value in a pure O2 plasma. The dispersive component showed the opposite behavior, going from 3.3 mJ/m2 before treatment to 24.4 mJ/m2 after exposure to the 85%N2-15%O2 plasma. On the other hand, no modification was observed for black spruce, probably because untreated samples already had a large dispersive component. Optical emission spectroscopy (OES) was used to understand the change in plasma properties leading to the observed variation of γPS and γDS. The gas temperature determined using the second positive system of N2 (C3Πu ν’=0 – B3Πg ν’’=2) was 320 ± 20 K and showed no trend with O2 concentration, thus ruling out variations due to thermal effects. Significant NO (A2Σ+ - X2Π) emission in the 225-305 nm range was observed in pure N2 plasmas. However, these bands disappeared with the introduction of O2, indicating that UV photons are not the prominent species driving the observed decrease in surface polarity. We also observed a strong increase of the N2+ (B3Σ u ν’=0 - X2Σ g+ ν’’=0) to N2 (C3Πu ν’=0 – B3Πg ν’’=2) bandhead intensity ratio with increasing O2 concentration. Such behavior is usually ascribed to an increase signature of the early afterglow and thus to an increase in the erosion rate of polymer surfaces [1]. In pure N2 plasmas, one expects N grafting to form nitrogen-containg groups which are likely to promote non-polar bonding [2]. As only a moderate decrease of γPS was observed in pure N2 and no change was observed in pure O2, it is believed that a combination of N grafting and surface erosion by oxygen atoms is required to achieve maximum modification of the surface polarity.
[1] M.K. Boudam et al., J. Phys D. 40, 1694 (2007)
[2] S. Vallon et al., J. Adhes. Sci. Technol. 10, 1287 (1996)