Characterization of PSS/PDADMAC-co-AA Polyelectrolyte Complexes and Their Stoichiometry Using Analytical Ultracentrifugation

Abstract

Analytical ultracentrifugation was successfully applied to the determination of the complex composition and characterization of the particles of water insoluble polyelectrolyte complexes between sodium poly(styrenesulfonate) (PSS) and copolymers of various ratios of diallyldimetylammonium chloride (DADMAC) and acrylamide (AA). Sedimentation velocity experiments in an analytical ultracentrifuge with absorption optics allow the observation of individual species in a system of strongly polydisperse, aggregated particles of colloidal level in the presence of free polymer. It was found that the complexes are remarkably polydisperse and form nonstoichiometric particles including the major component in considerable excess. The stoichiometry factor depends strongly on the ionic strength of the solution and the concentration of the components. At low initial mixing ratios and ionic strengths of about 10 -2 -10 -3 N, sedimentation equilibrium experiments can be performed. The results of the evaluation of free PSS and complex concentration gradients using the Ω-function are similar to the findings obtained with sedimentation velocity experiments. A model where secondary aggregates are surrounded by free polymers is discussed for the sedimentation of these particles. It is demonstrated that polyelectrolyte complexes with the copolymer containing 50% DADMAC and AA form comparatively monodisperse species in aqueous salt solution having sedimentation coefficients between 4 and 40 Sv.

Effect of a low-molecular-weight salt on colloidal dispersions of interpolyelectrolyte complexes

“…It is worth mentioning that the formation of similar aggregated structures was also observed for other pairs of oppositely charged polyelectrolytes, in particular, for Fig. 2 The dependence of the optical density OD 500 obtained for mixtures of P(DMDAAáCl) and P(MaáNa-co-Pr) on the concentration of NaCl OD 343 is the optical density measured at 343 nm and x is the distance from the meniscus of the sedimentation cell poly(sodium styrenesulfonate) and P(DMDAAáCl) [19,20].…”

“…4, 5). It is worth mentioning that similar inferences (but only for the case when the ionic strength of the surrounding medium is not extremely low) were drawn with respect to aggregated structures that appear as a result of electrostatic interaction between poly(styrene sulfonate) and P(DMDAAáCl) [19,20]. Table 1 contains the values of OD 500 obtained for the mixtures of P(DMDAAáCl) and P(MaáNa-co-Pr) prepared according to two dierent procedures, i.e., method A and method B, as well as the values of R H measured for the IPEC particles formed in these mixtures.…”

Effect of charge density on the formation and salt stability of polyelectrolyte complexes

“…[8,11] Electrophoretic light scattering, [24,25] viscometry [12] and analytical ultracentrifugation [26] showed excess binding of the major component and a corresponding overcharging of the PEC particles. Obviously, the PEC particles consist of a charge neutralized core surrounded by a shell of attached chains of the excess component, which stabilize the particles against further aggregation.…”

Polyelectrolyte complex formation in highly aggregating systems. Effect of salt: response to subsequent addition of NaCl

“…The strong ionic bindings and the high cooperativity result in frozen structures. Previous studies [9][10][11][12][13][14] showed that the PEC particles consist of a neutralized, stoichiometric core and a shell of the excess component, which stabilizes the particles against further coagulation. At the 1 : 1 mixing ratio of anionic to cationic groups macroscopic flocculation occurs.…”