Dynamics of initial stage flocculation of polystyrene latex spheres with polyelectrolytes

An end-over-end rotation apparatus was created in order to obtain reproducible mixing suitable for the study of the kinetics of flocculation. The validity was verified by measuring the rate of coagulation of monodispersed polystyrene latex particles with simple electrolytes by means of a Coulter Counter. The method was applied to the analysis of the initial behavior of flocculation induced by the addition of excess polyelectrolyte flocculant with a nominal molecular weight of 4.5 million. In contrast to coagulation with a simple electrolyte, the rate of flocculation in the initial stage was remarkably enhanced and then decreased abruptly after certain mixing steps. The degree of the initial stage of enhancement and the duration of this stage were found to be dependent on the concentration of the polyelectrolyte. Ascribing the enhancement to the increase in the effective collision radius of the colloidal particles due to the attached polymer layer, the thickness of this layer, delta(He), was calculated. Analyses showed that delta(He) increases as polymer concentration increases up to a layer thickness of 500 nm, which correlates with the size of the polymer in the solution. However, an analysis of the collision process between particles and polyelectrolytes implied that the kinetics of polymer adsorption in the initial stage are limited by transportation until near saturation. Taking into account the data on electrophoretic mobility, we concluded that our results are consistent with the picture of kinetically-controlled polymer adsorption proposed by De Witt and van de Ven [J.A. De Witt and T.G.M. van de Ven, Langmuir, 8 (1992) 788].