Wettability and spectroscopic characterization of silylated wood samples

Surfaces of three European wood species (namely, English oak, Hungarian oak, and Scots pine) and two tropical wood species (namely, teak and cloves) were silylated with dichlorodimethylsilane (DDS), dichlorodiphenylsilane (DPS) and octadecyltrichlorosilane (OTS) in the first step, and with chlorotrimethylsilane (CTMS) as a monofunctional reagent in a second step. Attenuated total reflection-Fourier transform infrared (ATR-FT-IR) and electron spectroscopy for chemical analysis (ESCA) measurements were performed in order to characterize the surface composition of the treated samples. The progress of surface modification was also monitored by contact angle measurements of different test liquids (water, formamide and diiodomethane). The water contact angles were found to be in the range of 80 degrees to 145 degrees. The most hydrophobic surface was obtained by two-step silylation by OTS and CTMS (water contact angles were between 131 degrees and 140 degrees). Interestingly, the hydrophobicity of DDS-treated samples showed a significant decrease after additional silylation by CTMS. The surface free energy values were evaluated in terms of the Lifshitz-van der Waals/acid-base theory. The results obtained by the surface analytical methods (i.e. FT-IR and ESCA measurements) were compared with the contact angle data. These results suggest that in the case of DDS-treated samples, CTMS molecules substitute partly the DDS molecules, thus only physisorption of the silylating agents is supposed at room temperature. Copyright (c) 2006 John Wiley & Sons, Ltd.