Water Molecule as a Dynamic Cross-Linker for Creating Multifunctional Poly(ionic liquid) Porous Membranes

ConspectusSupramolecular polyelectrolyte porous membranes (SPPMs), which structurally integrate supramolecular material properties, electrolyte characteristics and pore confinement effects into a membrane, represent an exciting class of materials targeted for a broad range of applications in modern science and technology. However, owing to the intrinsic water solubility of conventional polyelectrolytes and the complex bonding mode arising from their charged nature, a long-standing challenge in the field has been the development of reliable preparation methods for fabricating high-quality SPPMs with controllable pore architectures and programmable functionalities. There have been a few characteristic attempts at achieving SPPMs. One involves layer-by-layer assembly of polyelectrolyte species through the strategic utilization of "orthogonal" noncovalent interactions; the other involves self-assembly of amphiphilic polyelectrolyte block copolymers, forming SPPMs. However, considering the multiple tedious preparation steps, the use of large amounts of organic solvents, and/or expensive precursors, these approaches suffer from some inherent limitations for the scalable preparation of SPPMs. Undoubtedly, direct assembly of polyelectrolytes in water to produce SPPMs is a priority because of its eco-friendly nature and ease of scaling up.Poly(ionic liquid)s (PILs), i.e., polymerized ionic liquids, are a subclass of polyelectrolytes that combine some special characteristics of ionic liquids (ILs) with the common properties of polymers. Owing to their designable chemical structures, processability and mechanical/thermal stability, PILs have recently attracted considerable attention in both the polymer materials and membrane science fields. Our PIL materials chemistry group has long been engaged in the field of functional PIL porous membranes and has discovered a scalable, eco-friendly and technologically relevant method to produce SPPMs by simple water or vapor treatment of single-component homo-PILs. This straightforward fabrication strategy is capable of rationally designing varied SPPM materials for a diverse variety of applications.In this Account, we highlight the latest discoveries and proceedings related to SPPMs, particularly the unprecedented use of H2O molecules as dynamic cross-linkers to manufacture SPPMs by leveraging the chemistry of PIL materials. The design principle of PIL chemical structures on how to accurately control pore architectures and achieve programmable properties and functionalities of SPPMs will be systematically explored on the basis of the interplay between cation/anion and functional moieties. The formation mechanism of SPPMs is also discussed on the grounds of multiple characterization methods and theoretical calculations. The advanced applications of these SPPMs are interspersed throughout the Accouint. On the basis of these achievements, a future perspective of the challenges and opportunities for SPPMs is presented from the viewpoints of large-scale synthesis, functionalization and promising applications. This Accouint provides helpful guidance for the rational design of practical SPPM materials for versatile application scenarios.