Why do cationic polyacrylamides flocculate negatively charged particles?

The flocculation of negatively charged fine particles by high molecular weight cationic polyacrylamide occurs by the adsorption of the polyacrylamide chains on to the particle surface. Thus charge neutralization becomes a major mechanism, where the cationic polyacrylamides will locally reverse the particle surface charge.

How does polyacrylamide adsorb on kaolinite particles?

It was found that the amount adsorbed increased with increasing a polymer concentration. On the other hand, the adsorption behaviour of polyacrylamide on to kaolinite particles is dependent on the charge density of each polyacrylamide.

How does cationic polyacrylamide reduce zeta potential?

The reduction in the zeta potential to zero by the cationic polyacrylamide arises from charge neutralization through electrostatic attraction between the positively charged polymer and negative surface sites of the particle, and the adsorption of large amount of positively polymer onto the surface of kaolinite gives rise to charge reversal.

Where does polyacrylamide adsorption occur?

All authors have concluded that the adsorption of polyacrylamide occurs primarily onto the edge surface of kaolinite (i.e., on the broken bonds of aluminol (Al–OH) and silanol (Si–OH) groups) via hydrogen bonding, with Lee et al. stating that 94% of adsorption takes place at the edge surface.

Do cationic and anionic polyacrylamide settling rates increase with charge density?

The maximum settling rates of flocs produced by cationic and anionic polyacrylamides decrease with charge density and increase with molecular weight.

How do cationic polyacrylamides aggregate?

Thus charge neutralization becomes a major mechanism, where the cationic polyacrylamides will locally reverse the particle surface charge. Collision with negative patches on another particle allows bridging then aggregation .