CHARACTERIZATION OF THE SOL-GEL PROCESS USING RAMAN-SPECTROSCOPY ORGANICALLY MODIFIED SILICA-GELS PREPARED VIA THE FORMIC-ACID ALKOXIDE ROUTE

For precursor mixtures containing tetraethoxysilane (TEOS) and phenylt riethoxysilane (PhTREOS), time of gelation can be reduced by up to two orders of magnitude depending on reaction conditions employed when re acting the silicon alkoxide mixture with formic acid instead of water. Results indicate that time of gelation depends on the amount of PhTRE OS in the precursor mixture. Within the range of concentrations invest igated, an exponential law describes best the dependence of reduced ti me of gelation on the molar fraction of PhTREOS. Therefore, we conclud e that the phenyl ring acts as a steric hindrance to network formation . Raman spectroscopy is used to characterize the reaction between the alkoxide mixture and formic acid. During the acidolysis reaction, etha nol is formed as an intermediate. A preliminary reaction scheme is pro posed to account for the time dependence of species involved. Furtherm ore, Raman spectroscopy is successfully employed to monitor the effect s of post-gelation thermal treatment of the gel samples. The effects o bserved are interpreted with a model of a phenyl ring trapped in a sil oxane cage.