Initial stage of bridging flocculation of PSL particles induced by an addition of polyelectrolyte under high ionic strength

Dynamics of colloidal flocculation of polystyrene latex (PSL) particles induced by cationic polyelectrolyte was studied in order to evaluate the effective layer thickness of adsorbing polyelectrolyte under sufficiently high ionic strength, where charges in polyelectrolyte chains are substantially shielded. The size of polyelectrolyte in the solution, ap, was evaluated by the viscometry and by dynamic light scattering (DLS). Normalizing method of end-over-end rotation was adopted to analyze the initial-stage dynamics of flocculation. The rate of coagulation of monodispersed PSL particles induced by simple salt monitored by the Coulter Counter confirmed to be proportional to the initial number concentration, thus validating the method of analysis. Drimethylamino ethylmethacrylates with nominal molecular weights of 4.9 million and 2.0 million were tested as flocculants. In contrast to coagulation with a simple salt, the rate of flocculation just after the onset of mixing with polyelectrolyte was remarkably enhanced and then decreased or stopped abruptly after certain period. The protruding length of polyelectrolyte obtained from the enhancement of the rate of flocculation in the first stage, δHe, was found to be several times larger than the size of polyelectrolyte in bulk solution determined by viscometry and DLS. Stretched conformation of polyelectrolyte chain in the mixing flow condition is the reason for the formation of apparently thick adsorbed polyelectrolyte layer.