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

Abstract

The hybrid organic–inorganic system Tetra-ethyl-ortho-silicate functionalized with Octyl-triethoxy-silane, 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, because of 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 Octyl-triethoxy-silane, in the 1330–1450 cm−1 and 2725–3000 cm−1 ranges. Copyright © 2016 John Wiley & Sons, Ltd.