Sizing of PDADMAC/PSS complex aggregates by polyelectrolyte and salt concentration and PSS molecular weight

Herein we report on the influence of salt and polyelectrolyte (PEL) concentration, molecular weight, and mixing ratio on the size and size distribution of polyelectrolyte complex (PEC) particles composed of cationic poly(diallyldimethylammonium chloride) and anionic poly(styrene sulfonic acid). The unusual salt concentration dependence of PEC particle sizes was observed. This behavior was explained by competition of two processes both related to the charge screening: swelling/shrinking of the outer shell formed by the excess PEL molecules and increasing/decreasing of the aggregation rate of colloidal PEC particles. The results on the size regulation of PEC particles by varying PEL concentration reflect both competitive processes as well. The regulation of the mixing ratio of PEL allows producing PEC particles with different charges, and it does not affect significantly the PEC particle size regulation by salt concentration. The PEC size dependence on the molecular weight of polymer was shown to be power and an exponent value of α ≈ 0.13 was obtained for the spherical PEC particles. This value is lower than one for polymer particles with a compact globular structure with exponent values of α = 0.33. However, the molecular weight of only one polymer component of a two-component PEC particle was varied.