The influence of ionic strength and mixing ratio on the colloidal stability of PDAC/PSS polyelectrolyte complexes

Abstract

Polyelectrolyte complexes (PECs) form by mixing polycation and polyanion solutions together, and have been explored for a variety of applications. One challenge for PEC processing and application is that under certain conditions the as-formed PECs aggregate and precipitate out of suspension over the course of minutes to days. This aggregation is governed by several factors such as electrostatic repulsion, van der Waals attractions, and hydrophobic interactions. In this work, we explore the boundary between colloidally stable and unstable complexes as it is influenced by polycation/polyanion mixing ratio and ionic strength. The polymers examined are poly(diallyldimethylammonium chloride) (PDAC) and poly(sodium 4-styrenesulfonate) (PSS). Physical properties such as turbidity, hydrodynamic size, and zeta potential are investigated upon complex formation. We also perform detailed molecular dynamics simulations to examine the structure and effective charge distribution of the PECs at varying mixing ratios and salt concentrations to support the experimental findings. The results suggest that the colloidally stable/unstable boundary possibly marks the screening effects from added salt, resulting in weakly charged complexes that aggregate. At higher salt concentrations, the complexes initially form and then gradually dissolve into solution.

Sequestration of Methylene Blue into Polyelectrolyte Complex Coacervates

“…Precipitate formation was observed by eye only. It is known that order of mixing can influence the complexation process, and the evolution of coacervate and precipitate formation might be different under different conditions than reported here.…”

pH‐Controlled network formation in a mixture of oppositely charged cellulose nanocrystals and poly(allylamine)

“…In contrary, flexible chains form a globular “scrambled‐egg” structure with a spatial disorder of the PE chains . However, up‐to‐now, the behavior of macroscopic systems consisting of two oppositely charged PEs is an open question due to high system intricacy …”

Ability of the Poisson–Boltzmann equation to capture molecular dynamics predicted ion distribution around polyelectrolytes

“…The presence of ions can lead to responses such as shrinking, swelling, loosening, or even dissociation at high enough concentration. [20][21][22][23][24][25][26] Furthermore, the counterion type has been linked to the solubility, 27 kinetics, 28 stability, 29 and composition of PE complexes, [30][31][32][33] as well as their thermal response. 23 Most commonly, ion condensation in PE systems is described by Manning's theory, a mean field Poisson-Boltzmann (PB) description that models the polyion as an idealized, infinitely long line charge and the counterions within Debye-Huckel approximation.…”