Deciphering the Structure‐Performance Relationship of Polyamide Organic Solvent Nanofiltration Membranes via Synergistic Control of Monomer Geometry and Functionality

ABSTRACT Elucidating the structure‐performance relationship of polyamide (PA) nanofilms from monomer structure is essential for advancing organic solvent nanofiltration (OSN) membranes. However, most efforts focused on isolated molecular structure, lacking systematic structural control and rational guidance for the membrane fabrication. Herein, we employed a network‐based design strategy by selecting aromatic amine monomers with different configurations and functionalities to construct PA nano‐networks. Variations in monomer geometry and enhanced steric hindrance directed the topological growth of the polymer network and suppressed dense PA chain stacking, enhancing the porosity and solvent permeance of the membranes. Meanwhile, the membrane pore size can be further modulated to match the target solute by adjusting the monomer functionality. These insights established a cross‐scale structure‐performance relationship from monomer structure to network microstructure and ultimately to membrane performance. The optimized thin‐film composite (TFC) membrane fabricated with a star‐shaped trifunctional monomer (tris (4‐aminophenyl) amine, TAPA) exhibited exceptional permselectivity, with a methanol permeance of 13.96 L m −2 h −1 bar −1 and photosensitizer rejection of 99.38%. The TFC‐TAPA membrane achieved a 20‐fold greater enrichment efficiency for photosensitizer than a commercial OSN membrane. This work provides molecular‐level insights and guidance for the rational design of high‐performance OSN membranes through monomer geometry and functionality control.