Effect of mixing intensity on flocculation kinetics of polystyrene latex particles with high-charge density polyelectrolyte at various ionic strengths

Effect of mixing intensity on the flocculation kinetics of polystyrene latex (PSL) particles with a high-charge density polyelectrolyte was analyzed using a small stirred vessel equipped with a four-paddle impeller and four baffles. The intensity of mixing was estimated by the effective shear rate evaluated in terms of collision frequency between the colloidal particles. This estimation was performed by measuring the salt-induced rapid coagulation of PSL particles as a function of the rate of impeller rotation. Acrylamide-(dimethylamino)ethyl methacrylate methyl chloride with nominal molecular weight of 4.9×10⁶ g mol⁻¹ was used as a flocculant. An enhancement factor, determined by the ratio of the rate of flocculation with a polyelectrolyte in the initial stage to that of salt-induced rapid coagulation, was used as the evaluation index. It was found that the enhancement factor goes through a maximum with an increase in mixing intensity, thus implying the presence of an optimal mixing intensity for flocculation. Further, considerable fluctuation was observed for a low mixing intensity and the degree of fluctuation slightly increased as the ionic strength increased.