Non-equilibrium phenomena and kinetic pathways in self-assembled polyelectrolyte complexes

Abstract

Polyelectrolyte complexation has been conventionally focused on the thermodynamic states, where assemblies have equilibrated in solutions. Far less attention has been given to complex systems that are kinetically trapped at non-equilibrium states. A combination of time-resolved dynamic light scattering, small angle X-ray scattering (SAXS), and cryogenic transmission electron microscopy (Cryo-TEM) was employed here to investigate the internal structures and morphological evolution of non-equilibrium aggregates forming from a pair of two strong block polyelectrolytes over wide time and length scales. The role of formation pathways of electrostatically driven aggregates was assessed using two processing protocols: direct dissolution and salt annealing. The former led to thermodynamically stable products, while the latter resulted in kinetically trapped transient structures. After adding salt, the metastable structures gradually transformed into stable products. Cryo-TEM images showed the interconnected irregular morphologies of the aggregates, and SAXS data revealed the presence of fuzzy globular complexes with Rg ∼ 10 nm within them. A two-step process in the time-dependent structural transformation was found and characterized by a fast breakdown of interconnected transient aggregates followed by a slow redistribution of the incipient individual electrostatic assemblies. Furthermore, the prolonged aggregate disintegration process fitting to a stretched exponential function unveiled the broad relaxation distribution and significant structural heterogeneity in these polyelectrolyte complex nanoaggregates. This work brings new insight into the comprehension of non-equilibrium phenomena in self-assembled electrostatic assemblies and represents a first step toward constructing far-from-equilibrium polyelectrolyte complexes de novo for future applications.

Mechanism of Dissociation Kinetics in Polyelectrolyte Complex Micelles

“…Similar results have been found and reported by us in kinetically trapped polyelectrolyte complexes. 36 Satisfactory fits are only obtained when we fit the dissociation of the micelles with an Avrami-type model in the form of a compressed exponential function as follows:…”

“…In this article, we aim to make strides toward understanding the mechanism of dis- . 35,36 The subscripts indicate the numbers of repeat units. The PVBTMA block has been demonstrated as an effective cationic vector for DNA encapsulation and delivery, while the PAA block has been extensively studied as a proxy for weakly charged biomacromolecules.…”

Effects of Non-Electrostatic Intermolecular Interactions on the Phase Behavior of pH-Sensitive Polyelectrolyte Complexes

“…For instance, they have been employed as prototypes in reversible morphological phase transitions, 10,11 fabricated into hollow microcapsules and intertwined membranes by injection suspension or electron spinning, 8,12,13 and formulated into therapeutic delivery micelles [14][15][16] as well as biocompatible hydrogels. 9 Several experimental 13,[17][18][19][20][21][22][23] and theoretical studies [24][25][26][27][28][29][30][31] in recent years have investigated the thermodynamics 23,32,33 and kinetics 34,35 of polyelectrolyte complexation, focusing on the influence of electrostatic interactions and the concomitant entropic gains from the release of counterions upon complexation. Only a handful of theoretical and simulation works have investigated the influence of polymer-solvent interactions on the phase behavior of complexes.…”

Effect of mixed solvents on polyelectrolyte complexes with salt

“…The "as prepared" polymer concentration was fixed at~1 wt% (10 mg/ mL). Following the protocol of the direct dissolution method [30], we added stock solutions of polycations and polyanions sequentially to a solution with desired amounts of NaBr stock solution (5 M) and co-solvent of Milli-Q water and ethylene glycol or ethanol. After all the solutions were added, samples were immediately vortexed for at least 30 s.…”