Predicting Polyelectrolyte Coacervation from a Molecularly Informed Field-Theoretic Model

Abstract

Understanding the phase behavior of polyelectrolyte coacervation is crucial for many applications, including consumer formulations, wet adhesives, processed food, and drug delivery. However, in most cases, modeling coacervation is not easily accessed by molecular simulation methods due to the long-range nature of electrostatic forces and the typically high molecular weights of the species involved. We present a modeling strategy to study complex coacervation leveraging the strengths of both particle simulations and polymer field theory. Field theory is uniquely suited to capture larger-length scales that are inaccessible to particle simulations, but its predictive capability is limited by the need to specify emergent parameters. Using model coacervate-forming systems consisting of poly(acrylic acid) and poly(allylamine hydrochloride), we show an original way to use small-scale, all-atom simulations to parameterize field-theoretic models via the relative entropy coarse-graining approach. The dependence of coacervation on the salt concentration, molecular weight, and charge stoichiometry is predicted without fitting to experimental data and is consistent with experimental trends including asymmetric phase behavior from non-stoichiometric mixtures of polyelectrolytes. This demonstrates a unique simulation approach to study phase behavior in coacervate-forming systems, which is particularly useful when chemical specificity is of interest.

Exploration of Phase Behavior in Asymmetric Semiflexible Polyelectrolyte Mixtures Using Polymer Field Theory

“…73 These analyses have been performed using experiment, 30,36,37,72−74 theory, 44,69,71 and simulation. 68,70,75 Capturing the multifaceted phase behavior that manifests in polyelectrolyte systems with five components presents a formidable challenge, given the considerable domains that can be investigated. A prevalent approach, as evidenced in the literature, 57,66,67 leverages 3D diagrams to encapsulate a broad spectrum of polyelectrolyte phase behavior.…”

“…Symmetric systems have proven easier to work with mathematically but fail to grasp the importance of asymmetry that appears in most real solutions. Asymmetric polyelectrolyte solutions have been investigated for differences in polymer concentration, ,− length, ,, charge density, ,, flexibility, and ion valency . These analyses have been performed using experiment, ,,,− theory, ,, and simulation. ,, …”

Effects of Salt on Phase Behavior and Rheological Properties of Alginate–Chitosan Polyelectrolyte Complexes

“…The phase behavior in these systems results from a complex interplay between factors such as polymer chemistry, chain length, polymer concentration, charge ratio, temperature, pH, and ionic strength. ,,, The alteration in ionic strength of the media caused by the addition of salts (salt doping) can also alter the phase behavior. , It has been shown that increased salt concentration leads to phase transformation from solid precipitates to liquid coacervates and then to a homogeneous solution. ,, The mechanical responses of the complexes and their phase behavior with changing salt concentrations have been investigated by employing shear rheometry. ,, …”

“…Most of the investigations on the phase behavior of PECs in the literature involve a limited selection of synthetic polyelectrolytes. In contrast, studies on the phase change of natural polyelectrolyte complexes with the addition of salt are limited. ,− ,, Natural polyelectrolytes with high molecular weight, stiffer backbones, and long-range ionic interactions are expected to behave differently than synthetic polyelectrolytes. The formation of PECs from biopolymer pairs can be seen in several living systems responsible for various biological functions .…”

Coacervate or precipitate? Formation of non-equilibrium microstructures in coacervate emulsions

“…Strategies to control non-equilibrium behavior of synthetic PEC coacervates remain primitive, with the exception of ATP-fuelled time control of LLPS in specific chemistries. 14 In synthetic systems, the majority of coacervate research has aimed to characterize, model, and predict the complicated equilibrium phase behavior [15][16][17][18][19] and equilibrium rheology [20][21][22][23][24][25][26][27] of model coacervate-forming chemistries. Several pioneering studies established that titration order [28][29][30][31][32][33][34][35] and mixing efficiency 36 of polyanion, polycation, and salt can affect molecular-level structure.…”