Study of the action of formamide on the evolution of a sol by pH measurements and Fourier transformed infra-red spectroscopy

Abstract

Abstract pH measurements and Fourier transformed infrared spectroscopy (FTIR) were used to investigate the influence of formamide on the acid-catalyzed sol-gel process at 40°C. Two sols were studied: one containing formamide and the other not. Formamide, by reacting with the catalyzing protons was found to increase the sol pH, thus modifying the condensation reaction conditions. FTIR studies showed that in the presence of formamide condensation first, preferentially, leads to small oligomers of less than six Si atoms. These oligomers then condense and thus increases the degree of cross-linking of the gel network. The structure of the silica thus formed evolves towards the structure of vitreous silica. In the sol without formamide, condensation leads to long linear chains with little cross-linking. The gel will only have the interconnected structure of vitreous silica after calcination.