Rheological characterization of the gel point in sol-gel transition

The gelation of hydrolyzed alcoholic solutions of acetic acid modified titanium isopropoxide has been analyzed through rheological measurements. A new method is proposed for determining the chemical gel point of these systems that fail to obey the Chambon-Winter criterion. The suggested method is based on defining the gel point as the instant at which the variation of the viscoelastic function tan 6 with frequency is minimum. The influence of the sol composition on the gel point has also been investigated. The correlation between the gelation time and the examined compositional parameters, i.e. the modification and hydrolysis molar ratios, is reported. It can be concluded that the initial sol composition has a strong effect on the kinetics of the gelation process, but it does not significantly affect the gelation mechanism. (c) 2006 Elsevier B.V. All rights reserved.