Growth of polyelectrolyte complex nanoparticles: Computer simulations and experiments

Herein we report on simulation and experimental studies on the formation of monomodal polyelectrolyte complex (PEC) nanoparticles, prepared by mixing two solutions of oppositely charged polyelectrolytes (PELs) under variation of ionic strength and applying centrifugation. This work aims at the better understanding of recently reported experimental studies, which demonstrated that consecutive centrifugation results in the removal of small primary PEC particles in polymodal dispersions and receipt of monomodal PEC dispersions of secondary PEC particles. In order to describe this effect and the possibilities of particle size regulation in PEC dispersions, a novel particle coagulation model, based on the combination of the mean-field theory of Smoluchowski and the Fuchs stability approach including a classical DLVO potential of interparticle interactions, was used in this study. The aggregation process was simulated under variation of the typical colloidal parameters: the Hamaker constant A, the Debye length λ, and the ζ-potential. The influence of these parameters on the mean final size, kinetics, and size distribution function of the colloid particles was studied. In the experimental section we study the system of cationic poly(diallyldimemylammonium chloride) (PDADMAC) mixed with an excess of anionic sodium poly(styrenesulfonate) (PSS) and varying NaCl concentration in the range C_NaCl = 0.001-0.05 M. The size of secondary PEC particles as a function of the salt concentration exhibited a pronounced minimum at C_NaCl ≈ 0.005 M. The influence of PEL conformation on the PEC particle size and the comparability of simulation and experimental results are discussed.