SHEAR-INDUCED AGGREGATION OF CARBOXYLATED POLYMER LATICES

Orthokinetic flocculation of latex particles containing high levels of surface carboxylation was studied by shearing for short times in a rotational viscometer and measuring changes in particle size using photon correlation spectroscopy. Results can be interpreted in terms of a comparison between the DLVO repulsive force between a pair of particles and the hydrodynamic shear force opposing it. This enables a prediction of the critical shear rate, gamma(crit), required to initiate aggregation. Experimental and calculated values of gamma(crit) showed good agreement. The stability of the carboxylated latices under shear was much reduced at pH values > 7 when the surface groups are ionised. The increase in suspension viscosity with pH was shown to be critical in determining the onset of aggregation via hydrodynamic forces.