Ultrathin polyurea nanofilms via interfacial self-polymerization

Interface polymerization (IP) is the most attractive technology for the preparation of advanced separation membrane materials. However, conventional interfacial polymerization relies on diffusion-controlled reactions between amine and acyl chloride monomers, posing challenges in precise structure control for thin-film composite membranes. This work introduces an original interfacial self-polymerization (ISP) strategy using multifunctional aromatic isocyanate as single monomer at aqueous-organic interface. Distinct from IP's dual-monomer complex diffusion-reaction mechanism, ISP proceeds through unique self-limiting kinetics: isocyanates hydrolysis generate amines, which promptly react with adjacent unhydrolyzed isocyanates to form rigid crosslinked polyurea networks, hindering further isocyanate hydrolysis and finally achieves sub-10 nm thickness control (6–10 nm). The composite membranes via ISP exhibit excellent organic solvent nanofiltration performance: methanol permeance of 25.3 L m ^-2 h ^-1 bar ^-1 while molecular weight cut-off below 350 g mol ^-1 , surpassing most state-of-the-art membranes. This work establishes a novel platform strategy for fabricating ultrathin nanofilms and demonstrates its superior precision in thickness control.