Mechanistic Understanding of CO2 Adsorption and Diffusion in the Imidazole Ionic Liquid–Hexafluoroisopropylidene Polyimide Composite Membrane

The integration of molecular design and imidazole ionic liquids produces a synergistic effect to enhance and fine-tune the molecular sieve capability of polyimide (PI) membranes. The most difficult problem was to choose the right ionic liquids and moderate polymer combination. In this work, a series of systems of CO2 in [EMIM][Tf2N], [EMIM][BF4], and [EMIM][PF6] composited with 6FDA-based PI with different IL concentrations were discussed by all-atom molecular dynamics simulations. The results indicated that the CO2 diffusion coefficient decreases with the compatibility of the PI structure with CO2 molecules and increases with an increased IL concentration of up to 75 wt %. Therefore, this study may provide guidance for the design of PI membranes.