Rheology of titanium oxide based gels: determination of gelation time versus temperature

The gelation of hydrolysed alcoholic solutions of acetylacetone complexed t itanium butoxide was studied through rheological measurements. The gelation time was determined through the evolution of the storage and the loss modu li versus time at several frequencies using the Winters criteria. Fractal d imensions determined from rheological measurements are very close to self-s imilarity exponents obtained from SAXS experiments (d(f)= 2.4 +/- 0.1) and correspond to bushy structures. The effects of temperature and hydrolysis r atio on gelation were also studied. Increasing hydrolysis ratio and/or temp erature speed up the kinetics of hydrolysis-condensation reactions and thus decreases the gelation time t(g) however at the expense of an efficient cr osslinking. Indeed at t = t(g) the titanium ore-polymers obtained at shorte r t(g) are less dense and less elastic than the networks formed at longer t (g). An apparent activation energy (around 120 kJ mol(-1)) which was found to be independent of hydrolysis ratio, was calculated from the values of ge lation times determined at various temperatures. (C) 2000 Elsevier Science B.V. All rights reserved.