Manipulating interfacial polymerization for polymeric nanofilms of composite separation membranes

Composite separation membranes are essential in the fields of water treatment, mass concentration, purification, solvent exchange, gas separation, energy storage and conversion. The ability of composite membranes to selectively transport water, ions, solvents and other species is derived from their active layers with excellent selectivity, which are ultrathin polymeric nanofilms on supporting substrates. Hence, the fabrication and manipulation of the selective nanofilms have been of a great interest for decades. Liquid to liquid interfacial polymerization (LL-IP) has been maintaining its dominance in synthesizing high-quality polymeric nanofilms. Nonetheless, some ambiguities still remain in this industrial friendly reel-to-reel process owing to reaction complexity, limiting its capability of precise controlling on physicochemical properties of resultant nanofilms, which are highly desired in many applications. In this review, we delve into this powerful yet intangible technique from physics, chemistry and material perspectives. To lay a groundwork for controlling structure and chemical properties of nanofilms, this review focuses on the effects of the intrinsic chemistry and extrinsic environment of LL-IP process. The corresponding mechanisms and fundamental principles are discussed by linking up relevant studies. In addition, the molecular-sieving performance of nanofilms synthesized under various conditions is briefly reviewed to help readers appreciate the correlation between structure, properties and performance. The existing challenges to be addressed are consequently identified and the future research directions are discussed accordingly.