Exploring the structure and desalination efficiency of polyamide reverse osmosis membranes through diacyl-chloride incorporation

Thin-film composite aromatic polyamide reverse osmosis membranes were fabricated by interfacial polymerization between m-phenylenediamine in the aqueous phase and mixed acyl chloride monomers in the organic phase on a porous polysulfone support. This work focuses on how diacyl-chloride incorporation affects membrane structure, surface physicochemical properties, and short-term brackish-water desalination. A series of PA I membranes with different IPC/TMC ratios were prepared to vary the relative contributions of TMC-derived network-forming segments and IPC-derived linear segments. ATR-FTIR and XPS were used to verify polyamide formation and characterize surface elemental composition and carboxyl-group contribution, while SEM, AFM, water contact angle, and representative zeta-potential measurements were used to examine morphology and selected surface physicochemical properties. Molecular dynamics simulations were conducted for selected PA I compositions to estimate the model-derived crosslinked-segment fraction, f CL, MD , which was compared with the short-term NaCl separation behavior. Because the experimental NaCl rejection decreased markedly when the IPC/TMC ratio was increased from PA I -(1:4) to PA I -(1:5), the transition is discussed as an apparent composition-dependent transition region between these two simulated descriptors. Because membrane thickness, roughness, apparent hydrophobicity, carboxyl-group contribution, surface charge, morphology, and possible packing/free-volume characteristics changed simultaneously, f CL, MD should be considered one correlated structural descriptor rather than an isolated controlling variable.