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Polyelectrolyte complexes (PEC) from poly(diallyl-dimethylammoniumchloride) PDADMAC and two different polyanions, formed in aqueous solution, were characterized by different methods (zetapotential, net content, turbidity) and applied as flocculants.The flocculation of clay was investigated by sedimentation measurement as well as by a dynamic method, using a Fibre Optical Flocculation Sensor. The results of both methods showed that the most important advantages of PEC were the high velocity of sedimentation and a very broad range of the optimum flocculation concentration. In spite of the differences in the complexforming behavior of the two polyanions used, no significant differences between complexes of the same composition but different polyanions are obtained. In contrast, the ratio of anionic to cationic charges is of great importance for the mechanism of flocculation.

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The influence of low-molecular-mass salt, namely NaCl, on the properties of interpolyelectrolyte complexes (PECs) formed as a result of interactions between poly(diallyldimethylammonium chloride)(PDADMAC) and copolymers of maleic acid with propene [P(MS-P)] or methylstyrene [P(MS-α-MeSty)] in their salt-containing nonstoichiometric mixtures has been studied by means of turbidimetry, quasi-elastic light scattering, and laser-Doppler microelectrophoresis. It has been found that stable dispersions of positively charged PEC particles could be prepared at low salt concentration. The hydrodynamic radius of these PEC particles formed at a salt concentration <0.05 mol/L was shown to be nearly constant and to be in the range of a few hundred nanometers. A pronounced salt-induced increase in their size was observed at higher concentrations of NaCl. The complex dispersions formed with P(MS-α-MeSty) are more stable to salt than dispersions formed with P(MS-P). The flocculation behavior of silica was investigated by use of such cationic PEC microparticles as well as by PDADMAC, a water-soluble linear polycation. It can be seen that in contrast to the results obtained with PDADMAC alone, the PEC microparticles are able to flocculate silica particles with a high velocity of sedimentation and in a very broad range of polymer concentration. A restabilization could not be observed at high polymer concentration. On the basis of the experimental results, different flocculation mechanisms were proposed.

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