Evolution of Two Acid Steps Sol-Gel Phases by FTIR Technology.

Abstract FTIR has been used to follow the evolution of a sol–gel preparation accomplished with two acid/acid steps. The reaction of methyltrimethoxysilane mixed with colloidal silica was taken as an example, aiming at proving the use of IR spectroscopy for the determination of reaction aspects like the kinetic behaviour that is essential for the scale-up of the application. The steps were carried out for 60 min each and samples were taken in each step at variable time intervals. For the spectroscopy analysis the dispersion samples were deposited on a spinning disc of KBr or ZnSe obtaining thin hybrid organic/inorganic films. The signals at 950 cm-1 and 1,000–1,100 cm-1 related to the hydrolysis and condensation reaction, respectively were recorded at variable time and their intensity normalised to the 1,273 cm-1band of Si-CH3 group not involved in the hydrolysis nor condensation reaction. The effects of pH and temperature have been investigated showing that reliable effective data on the reaction extent of SiO2-doped sol–gel dispersions can be obtained by the FTIR spectroscopy. The data have been supported and interpreted also by SEM observations. The reactions degree of the (poly)condensation sharply increases after the addition of more alkoxysilane. Short reaction times can be designed that could be compatible with industrial production.