Analysis of initial stage of colloidal particles flocculation induced by different degree branching polyelectrolytes

Abstract

Flocculation performance of polyelectrolytes is affected by their molecular branching. To unravel the mechanisms involved, we performed flocculation experiments of negatively charged polystyrene latex particles using three cationic polyacrylamide-based polyelectrolytes differing only in the degree of molecular branching. In the experiment, a simple linear chain molecule and two branched polyelectrolytes were tested. The initial rate of flocculation under the condition of standardized mixing, the value of resulted electrophoretic mobility of particles coated with polyelectrolytes, and their hydrodynamic layer thickness by means of particle tracking of Brownian motion were monitored to compare the effect of branching degree. The rate of flocculation was found to increase with an increase in the degree of branching, as corresponding to the hydrodynamic adsorbed layer thickness. These results suggested the importance of the relaxation process polymer chain from coil-like solution conformation to flattened adsorbed state on the surface of colloidal particles. Branched polymers retain their shape after arriving on the surface due to the presence of branches that disturb smooth movement resulting in slow relaxation on the surface of the colloidal particle. Subsequently, forming thick adsorbed layer and enhances the rate of flocculation. Thus, explaining the commonly observed trend where branched polymers achieve better flocculating abilities than linear ones.