Étude de la dynamique de croissance de revêtements nanostructurés multifonctionnels sur le bois par plasmas froids à la pression atmosphérique
The objective of this thesis is to achieve advanced fundamental study of plasmas aimed at the deposition of functional nanostructured coatings on wood. A particular emphasis is placed on dielectric barrier discharges (DBD) at atmospheric pressure that do not require expensive vacuum systems and therefore are more easily combined with an industrial approach of production chain. Throughout our research, we realized that the deposits on wood substrates present much more scientific and technological challenges than processes on conventional substrates. This can be explained by the micro and nanostructure, quite unique to this material that not only changes the physical and chemical properties of the plasma but also the thin films growth dynamics. In this context, from electrical and spectroscopic measurements, coupled with predictions of a collisional-radiative model, we first studied the influence of the presence of wood substrates on the physics of DBD. In the case of the helium plasma, we measured the outgassing effects of the substrate on the evolution of the electron temperature and the number density of atoms in a metastable level. We further demonstrated that the discharge could "localize" on some regions of the substrate, an effect attributed to spatial variations in the atom density of the substrate which directly influence the voltage applied locally to the gas, and consequently, the local values of the discharge current. Subsequently, we studied the addition of an organosilicon precursor in the plasma for plasma-enhanced chemical vapor deposition. We noted that the surface becomes highly hydrophobic with contact angles greater than 130° due to the deposition of organosilicon fragments. In addition, these coatings exhibit excellent dimensional stability, a result very promising for applications. In the presence of outgassing effects, however, we noted that the coatings exhibited an interfacial SiOx layer, paving the way for multifunctional coatings: barrier properties of the SiOx layer and hydrophobic properties provided by the topmost SiOCH layer. Finally, we attempted to integrate this knowledge and expertise in the field of cold plasma at atmospheric pressure to develop plasma jet configuration coatings rather than by direct exposure to the plasma
Dielectric barrier discharge Atmospheric-pressure plasmas Collisional-radiative model Multifunctional coatings Wood