A comparative analysis of surface structure and surface tension of hybrid silica films

Unsupported SiO2-based films have been prepared by cohydrolysis of methyltriethoxysilane (MTES) and tetraethoxysilane (TEOS) in different molar ratios. Analysis of surface structure and surface tension have been performed; FTIR-ATR (attenuated total reflectance) results were compared with results obtained from atomic force microscopy (AFM) and dynamic contact angle (DCA) techniques. The chemical nature of the exposed surface is discussed on the basis of calculations of surface tension components using different theoretical models. Due to the different sampling depth of the techniques used, a complete and original description of the surface structure of SiO2-based films is proposed. The relative ratio between the exposed groups SI-OH, Si-O- and Si-CH3 depends on the TEOS/MTES ratio. Increasing %MTES produces a decrease of Si-OH and Si-O- surface content. The surface of pure MTES derived film appears to be a flat and dense arrangement of Si-Me groups pointing outward.