Thermal evolution of hybrid sol-gel silica coatings:: A structural analysis

The sol-gel method has been increasingly used to prepare organic-inorganic hybrid coatings with both glass and polymeric properties by including alkylalkoxides with one or more non-hydrolizable groups in the precursor alkoxide solution. When using MTES and TEOS precursors, it was found that the increase in Si-CH3 bond concentration in the coating augments the critical thickness, and strongly affects other properties. The final methyl content depends on both the composition of the precursor solution and the thermal treatment for densification. But little is known about the effect of this organic group on the hybrid structure and microstructure of the coatings. In this work, the effect of methyl content on the film structure and the evolution of porosity are analysed by using ellipsometry and infrared spectroscopy. A theoretical correction of the refractive index of the film and a description of the thermal evolution of the coating structure are also proposed.