Salt effect on formation and properties of interpolyelectrolyte complexes and their interactions with silica particles

The influence of low-molecular-mass salt, namely NaCl, on the properties of intel-poly electrolyte 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-alpha-MeSty)] in their salt-containing nonstoichiometric mixtures has been studied by means of turbidimetry, quasi-elastic light scattering, and laser-Doppler microele ctrophoresis. It has been found that stable dispersions of positively charg ed PEC particles could be prepared at low salt concentration. The hydrodyna mic 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 n anometers. A pronounced salt-induced increase in their size was observed at higher concentrations of NaCl. The complex dispersions formed with P(MS-al pha-MeSty) are more stable to salt than dispersions formed with P(MS-P). Th e 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 PDAMAC alone , the PEC microparticles are able to flocculate silica particles with a hig h velocity of sedimentation and in a very broad range of polymer concentrat ion. A restabilization could not be observed at high polymer concentration. On the basis of the experimental results, different flocculation mechanism s were proposed.