The rheol. of aqueous SiO2 dispersions was examined as a function of pH, fraction of SiO2, etc. A gradual transition from Newtonian to pseudoplastic behavior was observed as the SiO2 content was increased. Plots of plastic viscosity (hPL) vs. SiO2 content shows a rapid increase in hPL above a crit. SiO2 concentration, which was dependent on the pH of the dispersion. These results are explained in terms of the interaction between the SiO2 particles and the size of the units, at pH = 4 showing an increase in yield value (tB), reaching a max. at hydrolyzed polyacrylamide (I) concentration corresponding to ~0.5 coverage. Thereafter, the yield value decreased with further increase in I coverage. Moreover, the rheol. results showed extensive hysteresis in the shear stress-shear rate curves, indicative of thixotropy. The results are explained in terms of bridging flocculation and partial reversibility of the flocculated structure. Because of the strong adsorption of I against solid particles changing into a weak one, solid particles shield the interaction of the polymer mols; therefore as I increases in hydrolytic degree, neg. thixotropy appears in the system. On the other hand, an excess degree of hydrolysis or higher concentration of I weakens neg. thixotropy.

Key words: POLYACRYLAMIDE, HYDROLYSIS, SUSPENSION, SUPERMOLECULAR STRUCTURE, RHEOLOGICAL PROPERTY, SILICON DIOXIDE