(518h) Molecular Understanding of Polyamide Membrane in Desalination at Equilibrium and Nonequilibrium States Using Molecular Simulations

Reverse Osmosis of cross-linked aromatic Polyamide (PA) membrane is one of the most promising techniques for water desalination. Since the atomic-scale structure is directly related to the performance of the membrane, Investigation through atomic scale simulation under both equilibrium & non-equilibrium condition is very important. A realistic model of cross-linked membrane has been developed by employing house developed hierarchical cross-linking procedure. The density distribution, water content uptake, pore-size distribution and salt rejection has been analyzed under equilibrium and non-equilibrium states. Our simulation shows pore size distribution with the majority of the pore radiuses around 0.20 nm, giving rise to the membrane’s water-ion selectivity. The feasibility of water-ion separation through such subnanopores is indeed controlled by the strength of the ions’ dehydration free energy in addition to the size of a hydration cluster. The results also demonstrated that hydrogen bonding among water molecules in formation of water chains in less crosslinked area facilitates their transfer through the PA membrane subnanopores. More importantly, we successfully simulated non-equilibrium transfer at the realistic pressure gradient and provided precise description of the process. Our study provides fundamental understanding of structure-function relationship for PA membrane, which is critical for the polymer membrane experimental design.