The rheological behavior of fumed silica dispersions in glycerol (GL) and polyethylene glycol (PEG) have been studied under steady and oscillation shear. The reversible shear-thinning and shear-thickening behaviors have been observed. The two dispersions all show obvious shear-thickening when the shear rate is higher than the critical rate (γ_^.＞γ_^.c), but when γ_^.＜γ_^.c, the GL system only shows slightly shear-thinning behavior, while the PEG system shows shear-thinning comparatively more obviously. The storage modulus G', loss modulus G" and tg δ have also been studied through oscillation stress shear. The magnitude of G" is larger than that of G' and tg δ＞1 for both of the systems in the range of stress studied, which shows that the systems mainly possess the viscous properties. Through “clustering” theory, the shear-thinning and the shear-thickening behaviors can be explained. The shear-thinning is due to the breakage of the steric continuous network structure and that the degree of the shear-thinning of the PEG system is larger than the GL system is due to the less number of the hydrogen bonds and the laxation of the PEG chains; the shear-thickening is caused by the formation of the clusters.

Key words: silica dispersion, rheological property, shear-thickening, mechanism