RHEOLOGICAL BEHAVIOR OF MODERATELY CONCENTRATED SILICA SUSPENSIONS INTHE PRESENCE OF ADSORBED POLY(ETHYLENE OXIDE)

Adsorption and flocculation properties have been investigated for a we ll-characterized aqueous system of precipitated nanometric silicabeads in the presence of a high molecular-weight poly(ethylene oxide). Part icular attention was given to the evolution of these properties with i ncreasing concentration. In addition, the corresponding consequences o n the rheological behavior in the homogeneous domains of the phase dia gram of the systems were studied. Important rheological effects can ac tually be obtained with such systems, even at moderate values of the v olume fraction of the dispersed phase (5 . 10(-3) less-than-or-equal-t o PHI less-than-or-equal-to 5 . 10(-2)). According to the adsorption l evel, the number of particles per macromolecular chain, and the free p olymer equilibrium concentration, quite different phenomena were obser ved such as rheopectic shear-induced gelation, Newtonian flow or thixo tropic shear-thinning.