Crosslinking degree of polyamide membranes: From determination to rational design

Polyamide (PA) membranes produced through interfacial polymerization are widely used in desalination, wastewater treatment, solvent purification, and ion separation applications. Among their structural characteristics, the degree of crosslinking is a critical yet underexplored parameter that influences pore size, free volume, chargeability, permeability-selectivity balance, and long-term stability. However, achieving precise control over the degree and structure of crosslinking remains challenging, primarily due to the uncontrollable nature of interfacial polymerization reactions. This review is the first to systematically focus on the crosslinking of PA membranes, including quantitative characterization methods for crosslinking degree, the impact mechanism of crosslinking on membrane performance, and recent advances in strategies for regulating crosslinking degree. Finally, we discuss the challenges associated with accurately characterizing, precisely controlling, and scaling up the crosslinked structure of PA membranes, and propose the integration of emerging technologies such as in-situ probing, data-driven modeling, and intelligent manufacturing to aid in the design of PA membranes with precisely engineered network architectures. This review offers new insights into the development of next-generation PA membranes with enhanced efficiency and sustainability for separation processes. • Crosslinking degree identified as the central determinant of PA membrane performance • Quantitative methods for crosslinking degree evaluation are systematically summarized. • Mechanistic roles of crosslinking degree in mass transport and durability are clarified. • Strategies for tuning crosslinking degree via monomer design and IP process control • Future opportunities include in-situ probing, data-driven modeling, and smart fabrication.