AVS 59th Annual International Symposium and Exhibition
    Plasma Science and Technology Monday Sessions
       Session PS+BI-MoA

Paper PS+BI-MoA11
Role of Substrate Outgassing on the Formation Dynamics of Either Hydrophilic of Hydrophobic Wood Surfaces in Atmospheric-Pressure, Organosilicon Plasmas

Monday, October 29, 2012, 5:20 pm, Room 24

Session: Applications of (Multiphase) Atmospheric Plasmas (including Medicine and Biological Applications)
Presenter: O. Levasseur, Université de Montreal, Canada
Authors: O. Levasseur, Université de Montreal, Canada
L. Stafford, Université de Montreal, Canada
N. Gherardi, Université de Toulouse, UPS, INPT, LAPLACE, France
N. Naudé, Université de Toulouse, UPS, INPT, LAPLACE, France
P. Blanchet, FPInnovations, Canada
B. Riedl, Université Laval, Canada
A. Sarkissan, Plasmionique, Canada
Correspondent: Click to Email
Dielectric barrier discharges (DBDs) were thoroughly investigated over the last several years with one of the main goals being the achievement of a homogeneous discharge at high operating pressure in various gas mixtures. This keen interest is mainly driven by the fact that atmospheric-pressure DBDs present major advantages over low-pressure plasmas for polymer treatments, one of the most important being the ability to work with cold plasmas without the use of high-end vacuum pumping systems. Over the last decade many precursors, such as organosilicon compounds like hexamethyldisilazane (HMDSN) and hexamethyldisiloxane (HMDSO), were added to these cold, atmospheric-pressure plasmas for PECVD applications and a wide variety of coatings have been obtained by such methods. Application of DBDs to the treatment of polymers is however much more challenging than for conventional substrates such as Si or SiO2. This can be not only be attributed to the highly complex chemical nature of most polymers but also to their generally porous microstructure which can release impurities in the discharge either from plasma-substrate chemical reactions or from sample outgassing (if not pumped-down beforehand). Such impurities can greatly alter the discharge stability and gas-phase kinetics which are both known to play an important role on the plasma deposition dynamics. In this work, we capitalize on the very porous nature of wood to examine the influence of substrate outgassing during PECVD on the stability of a N2-HMDSO discharge and on the evolution of the properties of plasma-deposited thin films over sugar maple and black spruce wood samples. Current-voltage characteristics revealed a transition from a filamentary to a homogeneous discharge with increasing plasma treatment time, t. Based on optical emission spectroscopy, the filamentary behavior was ascribed to the release of air and humidity from the wood substrate following plasma exposure which produced significant quenching of N2 metastables. This effect vanished at longer treatments times due to the nearly complete “pumping” of products from the substrate and the progressive deposition of a “barrier” layer. Analysis of the surface wettability through static, water contact angles (WCAs) and of the surface composition through FTIR and XPS indicated that for t < 10 min, the wood surface was more hydrophilic due to the formation of a SiOx layer, a typical behavior for HMDSO deposition in presence of oxygen. On the other hand, for t > 10 min, the static WCA increased from ~50º up to ~140º due to the deposition of hydrophobic Si(CH3)3-O-Si(CH3)2 and Si(CH3)3,2 functional groups.