Formation of mono-sized polyelectrolyte complex dispersions: effects of polymer structure, concentration and mixing conditions

By interpolyelectrolyte complexation of oppositely charged polymers in aqueous media homogeneous complex dispersions containing mono-sized nanoparticles could be prepared. In this study poly(diallyldimethylammonium chloride) (PDADMAC) is used in combination with copolymers of acrylamide and sodium acrylate (PR30US) and also of poly(maleic acid-co-propene) (P(MS-P)), which differ in their molecular weight, charge distance and charge density. The effects of polymer structure, concentration and mixing conditions were investigated by quasi elastic light scattering, polyelectrolyte titration and turbidity measurements. The experimental results show that both systems PDADMAC/ PR30US and PDADMAC/P(MS-P) form stable mono-sized complex particles if the starting component is deficient in the mixture. In this case the structural and kinetic parameters of the complex forming process are determined by the minor component that is completely bound by the oppositely charged polyions, forming a neutralized core and a stabilizing shell of the excess component. The stability of the formed complex dispersions dependent on the polymer concentration has also been followed. By using PDADMAC as starting solution and a fixed mixing ratio n -ln + = 1.1, the polymer concentration was varied in the range from 1 to 4.5 mmol l(-1). It could be shown that the size of the complex particles increases without change of the size distribution up to a critical polymer concentration c*. Above c* a pronounced increase of particle size and polydispersity index was observed. (C) 2003 Elsevier Science B.V. All rights reserved.