Interfacial Polymerization\nof Aromatic Polyamide Reverse\nOsmosis Membranes

Polyamide membranes are widely used in reverse osmosis\n(RO) water\ntreatment, yet the mechanism of interfacial polymerization during\nmembrane formation is not fully understood. In this work, we perform\natomistic molecular dynamics simulations to explore the cross-linking\nof trimesoyl chloride (TMC) and m-phenylenediamine (MPD) monomers\nat the aqueous–organic interface. Our studies show that the\nsolution interface provides a function of “concentration and\ndispersion” of monomers for cross-linking. The process starts\nwith rapid cross-linking, followed by slower kinetics. Initially,\namphiphilic MPD monomers diffuse in water and accumulate at the solution\ninterface to interact with TMC monomers from the organic phase. As\ncross-linking progresses, a precross-linked thin film forms, reducing\nmonomer diffusion and reaction rates. However, the structural flexibility\nof the amphiphilic film, influenced by interfacial fluctuations and\nmixed interactions with water and the organic solvent at the solution\ninterface, promotes further cross-linking. The solubility of MPD and\nTMC monomers in different organic solvents (cyclohexane <i>versus\nn</i>-hexane) affects the cross-linking rate and surface homogeneity,\nleading to slight variations in the structure and size distribution\nof subnanopores. Our study of the interfacial polymerization process\nin explicit solvents is essential for understanding membrane formation\nin various solvents, which will be crucial for optimal polyamide membrane\ndesign.