RHEOLOGY OF THE GELATION OF FLUORINE DOPED SILICA SOLS.

Small amplitude oscillatory shear measurements are used to probe the gelation kinetics of aqueous sols composed of particulate silica and silicon alkoxide solutions. Unlike steady shear measurements, these dynamic tests do not alter the structure and kinetics of the sol-gel process. The dynamic storage moduli of both systems show sharp transitions at the onset of gelation. However, the gelation kinetics of the two systems are very different: the modulus of the alkoxide system remains unchanged until the gel point is reached, whereas that of the particulate system increases with time even below the gel point as the colloid clusters grow. Unlike the alkoxide gel, the particulate gel reverses to a sol upon shearing.