Monitoring the polymerization process of Si-based superhydrophobic coatings using Raman spectroscopy

Abstract Water is the main deterioration factor of monuments and outdoor objects of the cultural heritage. The application of (super)hydrophobic siloxane coatings constitutes a promising method for monument protection and consolidation. In this study, the polymerization process, occurred because of the air humidity, of siloxane based (super)hydrophobic coatings is monitored at the molecular level using micro-Raman spectroscopy. Initially, we record the time evolution of changes in the structure of the commercially available pure poly(alkyl siloxane) Silres BS 290 (no solvent or nanoparticles) using micro-Raman spectroscopy. Then, the Raman study is extended to coatings prepared from solution of Silres BS 290 in white spirit. These coatings are hydrophobic according to contact angle measurements. Finally, Raman is employed to monitor the polymerization of two composite coatings prepared from dispersions of silica and tin oxide nanoparticles which were added in the siloxane solution. The resulting composite coatings exhibits superhydrophobic properties, according to contact angle measurements. Superhydrophobicity is interpreted in terms of a complex micro- and nanoscopic architecture, revealed using scanning electron microscopy. The aforementioned coatings are applied using a spraying method on glass and stone substrates, which have been used in monuments of the cultural heritage. The Raman results of this in situ analysis showed that certain peaks appearing in the high energy region of the spectra can be used as indices to monitor the polymerization process of the materials.