OctTES/TEOS system for hybrid coatings: real time monitoring of the hydrolysis and condensation by Raman spectroscopy

The hybrid organic-inorganic system Tetra-ethyl-orthosilicate (TEOS) functionalized with Octyl-triethoxy-silane (OctTES), studied as protective coating for the preservation of historical glasses from the environmental weathering agents, has been characterized by Raman spectroscopy by monitoring the sol-gel reactions over time through characteristic features in the spectrum. In particular, for the hydrolysis reaction the disappearance of the 653 cm-1 (Si-O symmetric breathing) and 810 cm-1 (CH2 rocking in Si-alkoxides) peaks and the growth of the 710 cm-1 band, due to hydrolyzed alkyl-silane, and of the 881 cm-1 peak (ethanol C-C symmetric stretching) have been checked. Moreover, the condensation reaction can be tracked by the disappearance of the two main peaks of the alcohols at 816 and 881 cm-1, going along with the growth of the broad band between 250 and 500 cm-1 (Si-O-Si symmetric bending) and of the feature at 840 cm-1 (Si-O-Si stretching). At the end of the condensation process the Raman spectrum still displays spectral bands unique to the alkyl chain in OctTES, in the 1330-1450 cm-1 and 2725-3000 cm-1 ranges.