THE STABILITY OF SILICA IN NONAQUEOUS MEDIA BY POLY-2-VINYL PYRIDINE POLY-TERT-BUTYL STYRENE BLOCK COPOLYMERS .2. RHEOLOGICAL STUDIES

The rheology of silica dispersions in an aromatic hydrocarbon solvent was investigated as a function of volume fraction, Φ, of the particles. All dispersions showed non-Newtonian flow within the Φ range 0.004-0.02, indicating a flocculated structure which probably forms a chain network within the dispersion. The rheology was also investigated in the presence of copolymers of poly-2-vinyl pyridine/poly-tert-butyl styrene (P2VP/PBS) (at full coverage) with weight average molecular weights of 4 200, 7 400 and 28 600. Only the low molecular weight polymer gave stable dispersions characterised by Newtonian flow. The other two polymers gave pseudoplastic dispersions which were not significantly different from those prepared in the absence of copolymer. The enhanced stability with the low molecular weight was thought to be due to its rapid diffusion and adsorption, thus breaking the silica chain aggregates. © 1990.