Perspective on the Processing and Functionalities of Solid-State Polyelectrolyte Complexes

The electrostatic complexation between oppositely charged polyelectrolytes leads to the formation of polyelectrolyte complexes (PECs) that can exist as aqueous dispersions, fluidic coacervates, or solid precipitates. Among them, PEC dispersions and coacervates have readily found extensive applications in encapsulation, drug delivery, gene therapy, and wet adhesion, among others. In contrast, solid-state PECs suffer from poor processability because they are normally insoluble and infusible, which limits their potential applications. Recent research has been increasingly devoted to improving the processability of solid-state PECs. A primary approach is enhancing spatiotemporal control over the complexation process, achieved by modulating pH, dielectric constants (ε), and salt concentrations in the dissolving solvents or by tailoring the chemical structures of polyelectrolytes. On the basis of these advances, novel methods (e.g., solution casting, extrusion, phase inversion, molding, additive manufacturing) have been explored to process solid-state PECs into structured materials, including membranes, porous materials, fibers, hydrogels, and more. These materials show promising applications in molecular separation, sensors, actuators, adhesives, barrier materials, flame retardants, and scaffolding, which are the focus of this Perspective.