Studies of the surface wettability and hydrothermal stability of methyl-modified silica films by FT-IR and Raman spectra

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• 作者：Jing Yang ; Jierong Chen ; Jinghua Song
• 关键词：Surface energy ; Wetting ; Surface structure ; Infrared absorption spectroscopy ; Raman scattering spectroscopy
• 刊名：Vibrational Spectroscopy
• 出版年：2009
• 出版时间：20 July 2009
• 年：2009
• 卷：50
• 期：2
• 页码：178-184
• 全文大小：284 K

文摘

Fourier transform infrared (FT-IR) and Raman spectroscopy were employed to study the hydrothermal stability and the influence of surface functional groups on the surface wettability of methyl-modified silica films. The surface free energy parameters of the silica films were determined using the Lifshitz-van der Waals/acid–base approach. The thermal decomposition mechanisms of the CH₃ groups in the methyl-modified silica material are proposed. The results show that with the increase of methyltriethoxysilane (MTES)/tetraethylorthosilicate (TEOS) ratio, the surface free energy and surface wettability of the silica films decrease greatly. This is mainly because of the contribution of the acid–base term; the intensity of Si–CH₃ groups increases at the expense of the intensity of O–H groups in the samples. The surfaces of the methyl-modified silica films exhibited predominantly monopolar electron-donicity. The contact angle on the silica film surface reaches its maximum value when calcination is performed at 350 °C. Thermogravimetric analysis implies that some low molecular weight species, such as H₂, CH₄, and C, are eliminated upon thermal decomposition of the –CH₃ groups. The Si–CH₃ and –CH₃ vibrational bands diminish in intensity as the calcination temperature is increased, disappearing completely when the calcination temperature is increased to 600 °C. When the calcination temperature is increased to 750 °C, the free carbon and CSi₄ species will be formed.