Structure and porosity of hybrid SiO2 coatings

Morphology and volumetric fraction of pores (V-p), determine several properties of sol-gel coatings. In this work, two methodologies for porosity characterisation of sol-gel hybrid SiO2 coatings as a function of starting compositions and thermal treatment conditions are proposed. V-p was determined from ellipsometric measurement of the refractive index (n). A theoretical correction of n for SiO2 for hybrid system is suggested by employing additive molar properties. An ET-IR method that involves the analysis and fitting of infrared spectra between 1300-960 cm(-1) is derived from previous results. From the thermal evolution of the FT-IR spectra different signals and its evolution were assigned to optical modes activated by porosity and SiO2 network densification. Correspondence between thermal evolution of porosity obtained by means of both of the studied methodologies supports these assignments.