Deposition of Hydrophobic Functional Groups on Wood Surfaces Using Atmospheric-Pressure Dielectric Barrier Discharge in Helium- Hexamethyldisiloxane Gas Mixtures

O. Levasseur, Prof. L. Stafford Departement de Physique, Universite de Montreal, Montreal (Quebec) H3C 3J7, Canada E-mail: luc.stafford@umontreal.ca N. Gherardi, N. Naude Universite de Toulouse, UPS, INPT, LAPLACE, F-31062 Toulouse Cedex 9, France N. Gherardi, N. Naude CNRS, LAPLACE, F-31062 Toulouse Cedex 9, France V. Blanchard, P. Blanchet FPInnovations – Division des Produits du Bois, Quebec (Quebec) G1P 4R4, Canada B. Riedl Centre de Recherche sur le Bois, Universite Laval, Quebec (Quebec) G1K 7P4, Canada A. Sarkissian Plasmionique, Varennes (Quebec) J3X 1S2, Canada This work examines the functionalization of sugar maple (Acer saccharum) and black spruce (Picea mariana) wood surfaces using an atmospheric-pressure dielectric barrier discharge in He and He/HMDSO (hexamethyldisiloxane) gas mixtures. Wood samples were placed on one of the electrodes and the plasma was sustained by applying a 3.5 kV peak-to-peak voltage at 12 kHz. Analysis of the discharge stability through current–voltage (I–V) characteristics revealed a filamentary behaviour, in sharp contrast with the homogeneous He discharge obtained with a glass sample. Optical emission spectroscopy performed near the wood vicinity revealed strong N2 and N þ 2 emissions, suggesting that wood outgassing plays an important role in the evolution of the discharge regime. Analysis of the surface wettability through water contact angle (WCA) measurements indicated that freshly sanded wood samples treated in He/HMDSO plasmas became more hydrophobic with WCAs in the 1208–1408 range depending on treatment time and wood species. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy measurements on samples exposed to He/HMDSO plasmas revealed the deposition of hydrophobic Si(CH3)3-O-Si(CH3)2, Si(CH3)3 and Si(CH3)2 functional groups as well as an increase of the CH-to-OH band intensity ratio. For relatively thick coatings, the WCA following natural aging under uncontrolled conditions remained constant at 1328 38 which highlights the stability of the plasma-deposited thin films, a very promising result for structural and decorative outdoor applications.