A molecular simulation protocol for swelling and organic solvent nanofiltration of polymer membranes

Polymer membranes have received considerable interest for organic solvent nanofiltration (OSN). The OSN performance is governed by many complex factors and quantitative understanding is experimentally challenging. In addition, it is a prerequisite to characterize membrane swelling in solvents prior to nanofiltration. A molecular simulation protocol is developed herein to investigate the swelling of three polymer membranes namely polybenzimidazole (PBI), polyimide (PI) and polymer of intrinsic microporosity (PIM-1) in four organic solvents (methanol, ethanol, acetonitrile and acetone), and then examine the OSN through the swollen membranes. The simulation protocol can highly efficiently simulate membrane swelling, which is approximately one order of magnitude faster than normal simulation method. The predicted swelling degrees of the three polymer membranes follow experimentally measured trend, exhibit good relationships with the polymer-solvent solubility parameter differences and the mean pore sizes of swollen membranes. For the OSN of a dye (methylene blue) in the four organic solvents, 100% rejection is found by the swollen PBI, PI and PIM-1 membranes. The predicted solvent permeabilities through PIM-1 and PI membranes match fairly well with experimental data, and their dependences on solvent viscosity, pore size and polymer-solvent interaction are examined. From this simulation study, the microscopic insights into the swelling of polymer membranes and the permeation of organic solvents are provided, which are useful for the development of new membranes for high-performance OSN.