Saloplastics and the polyelectrolyte complex continuum: Advances, challenges and prospects

Polyelectrolytes (PEs) are macromolecules that possess repeating units of ionizable groups in addition to counterions. Polyelectrolyte complexes (PECs) emanate from the entropy-driven self-assembly interactions between oppositely charged PEs. Saloplastics (salt-processed PECs) have attracted significant interests as highly promising functional materials for many applications in recent years. This review critically examines the general PEC continuum and discusses processing progress and application in key scientific fields, including pharmacy, biomedicine, energy, electronics, environment and food, with major focus on saloplastics. Here, PEs are classified and distinctions are made among complexes, coacervates and solutions. Detailed discussions of the factors that affect processing and strategies to overcome same are presented. In general, PECs from synthetic origins are largely utilized in energy and electronic applications due to their excellent conductivity, stretchability and self-healing properties, whilst those from natural sources are employed in pharmaceutical, biomedical and food applications owing to their non-toxicity and biocompatibility. PECs have also been applied as supporting materials to retard flammability and prevent CO₂ flooding. A current surge in saloplastic PEC research, particularly over the past few years presents good prospects for the future towards unraveling their many intriguing properties.