SOL FORMATION RATES IN ACID-CATALYZED TITANIUM ISOPROPOXIDE WATER REACTION IN ISOPROPANOL

Acid catalyzed sol-forming reactions of titanium isopropoxide with wat er in isopropanol solutions were investigated by quasielastic light sc attering (QELS) and viscosity measurements. Light scattering was used to determine the dependence of the intensity average mean diameter on time during the sol formation. The rate of increase of the specific vi scosity was also determined. The rates of increase of diameter and spe cific viscosity exhibited similar complex dependencies on the HCl cata lyst concentration; a minimum near 10 mM with a second decrease as the HCl concentration approached 100 mM. The dependence of these rates on the concentration of the acid catalyst was qualitatively similar to p atterns observed for acid catalyzed sol formation by the reaction of s ilicon alkoxlides with water. The difference in the rates of increase of the colloid diameter and the specific viscosity was used to estimat e the fractal dimension of the colloid during the sol formation. In th e range of HCl concentration corresponding to a minimum in diameter gr owth rate, 5-20 mM for these solutions, the colloid species had fracta l dimensions near 2. At acid concentrations increasing and decreasing from this range the fractal dimension increased to approach 3. (C) 199 8 Elsevier Science B.V. All rights reserved.