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Complex coacervation, a liquid–liquid phase separation phenomenon driven by electrostatic interactions between oppositely charged polyelectrolytes (PEs), has attracted widespread attention because of its relevance in biological systems and potential applications in materials science. Although many theoretical models, experimental investigations, and computational studies have investigated the thermodynamics, phase coexistence behavior, and rheological properties in great detail, a molecular-level understanding of the internal structure of the complex coacervate phase is still lacking. In this study, we investigate the effects of the degree of polymerization of the polyelectrolytes (N) on the phase behavior and internal structure of the resulting coacervate phase using molecular dynamics simulations employing a simplistic bead–spring model of polyelectrolytes and explicit nonpolar solvents. Our simulations show an increase in coacervate phase stability with N, elevating the critical temperature in agreement with existing theoretical predictions and experimental observations. The polyelectrolytes inside the dense phase maintain a homogeneous overlapping distribution without collapsing into globules. The compactness of the dense phase increases with N in agreement with prior experimental observations, despite a concomitant increase in the polymer’s effective size as quantified by its radius of gyration (Rg). We discuss the implications of this model for a fundamental understanding of the coacervation process and as a first step toward the systematic examination of the mutual role of electrostatics and chemistry in the behavior of solvated polyions. 

We report the synthesis of catechol-functionalized symmetric triblock polymers comprising densely functionalized catechol endblocks using anionic ring-opening polymerization (AROP) and thiol–ene click chemistry. 

The stabilization of complex coacervate microdroplets can be modulated by the concentrations of cPE stabilizer and salt, enabling their various applications, such as bioreactors, drug delivery vehicles, and encapsulants. 

Polyelectrolyte complex (PEC) hydrogels, which self-assemble via complexation of oppositely charged block polymers, have recently risen to prominence owing to their unique characteristics such as hierarchical microstructure, tunable bulk properties, and the ability to precisely assimilate charged cargos (i.e., proteins and nucleic acids). Significant foundational research has delineated the structure−property relationship of PEC hydrogels for use in a wide range of applications. In this Perspective, we summarize key findings on the microstructure and bulk properties of PEC hydrogels and discuss how intrinsic and extrinsic factors can be tuned to create specifically tailored PEC hydrogels with desired properties. We highlight successful applications of PEC hydrogels while offering insight into strategies to overcome their shortcomings and elaborate on emerging opportunities in the field of electrostatic self-assemblies. 

Aqueous two-phase systems (ATPS) are useful in various applications, from purification and separation of biomolecules to wastewater treatment. While they have great utility on their own, there is great interest in discovering how their emulsions, comprising droplets of one aqueous phase dispersed in the other aqueous phase, might be stabilized to enhance their functionality and applications. There are several examples of these systems, but the two most common systems found in the literature are PEG–dextran and complex coacervate ATPS. In this Review, we discuss these systems, their utility, and many different approaches for stabilizing their water/water (w/w) emulsions. We highlight examples wherein interfacial stabilizers such as liposomes, polymers of diverse architectures, colloids of varied shapes and morpholo- gies, and even whole cells have been employed. These stabilization approaches for both PEG–dextran and complex coacervate ATPS are discussed. We conclude with a discussion of the applications of these ATPS and how they can benefit from the creation of corresponding w/w emulsions with stabilized droplets. 

Dynamic light scattering (DLS) is a commonly used analytical tool for characterizing the size distribution of colloids in a dispersion or a solution. Typically, the intensity of a scattering produced from the sample at a fixed angle from an incident laser beam is recorded as a function of time and converted into time autocorrelation data, which can be inverted to estimate the distribution of colloid diffusivity to estimate the colloid size distribution. For polydisperse samples, this inversion problem, being a Fredholm integral equation of the first kind, is ill-posed and is typically handled using cumulant expansions or regularization methods. Here, we introduce a user-friendly graphical user interface (GUI) for analyzing the measured scattering intensity time autocorrelation data using both the cumulant expansion method and regularization methods, with the latter implemented using various commonly employed algorithms, including NNLS, CONTIN, REPES, and DYNALS. The GUI allows the user to modulate any and all of the fit parameters, offering extreme flexibility. Additionally, the GUI also enables a comparison of the size distributions generated by various algorithms and an evaluation of their performance. We present the fit results obtained from the GUI for model monomodal and bimodal dispersions to highlight the strengths, limitations, and scope of applicability of these algorithms for analyzing time autocorrelation data from DLS. 

Photocrosslinkable precursors (small molecules or polymers) undergo rapid crosslinking upon photoirradiation, forming covalently crosslinked hydrogels. The spatiotemporally controlled crosslinking, which can be achieved in situ , encourages the utility of photocrosslinked hydrogels in biomedicine as bioadhesives, bioprinting inks, and extracellular matrix mimics. However, the low viscosity of the precursor solutions results in unwanted flows and dilution, leading to handling difficulties and compromised strength of the photocrosslinked hydrogels. Here, we introduce oppositely charged triblock polyelectrolytes as additives for precursor solutions that transform them into self-assembled polyelectrolyte complex (PEC) hydrogels with enhanced shear strength and viscosity, providing interim protection against precursor dilution and mitigating secondary flows. The PEC network also augments the properties of the photocrosslinked hydrogels. Crosslinking of the precursors upon photoirradiation results in the formation of interpenetrating polymer network hydrogels with PEC and covalently-linked networks that exhibit shear moduli exceeding the linear combination of the moduli of the constituent networks and overcome the tensile strength–extensibility tradeoff that restricts the performance of covalently-linked hydrogels. The reinforcement approach is shown to be compatible with four types of photocrosslinkable precursors, does not require any modification of the precursors, and introduces minimal processing steps, paving the way for a broader translation of photocrosslinkable materials for biomedical applications.