Response of polyelectrolyte complexes to subsequent addition of sodium chloride: Time-dependent static light scattering studies

The applications of polyelectrolyte complexes range from large-scale industrial products to special uses in biotechnology and medicine, yet one significant problem is their instability against changes in their environmental conditions, particularly the addition of salts. This concerns the colloidal stability as well as the stability of ionic bindings. Previous work on the effect of sodium chloride revealed that not only additional aggregation, but: also complete dissolution may occur, depending on the nature of the polyelectrolyte components used. In these studies, the systems required up to one hour to become stable. Multi-angle static light scattering was used to investigate the processes taking place after the addition of NaCl to polyelectrolyte complexes (PEC) formed in pure water. PECs were prepared with polymethacrylate as polyanion and poly(dallyldimethylammonium chloride) and a copolymer of this polycation with 53 mol-% of acrylamide. These systems were chosen because of their interesting behavior: secondary aggregation, swelling, and dissolution at a critical salt concentration. The time-dependence of these effects was studied in detail by static light scattering.