Influence of Polymer Chain Length on Structural Properties of Carbon Molecular Sieving Membranes and Their Effects on Co2, Ch4 and N2 Adsorption: A Molecular Simulation Study

Carbon molecular sieving membranes (CMSM) derived from 6FDA/BPDA-DAM polymer precursors (6F-CMSM) show excellent adsorption and selectivity towards CO 2 . Using molecular dynamics (MD) simulations, we investigate how the length of individual polymer chains determines the morphologies emerging from the same monomers. Smaller chains produce densely packed structures, whereas longer chains arrange in layers, creating larger voids comprising both micropores and ultra-micropores. The pure gas adsorption isotherms of CO 2 , CH 4 , and N 2 inside various 6F-CMSM morphologies, obtained from MD, provide theoretical insights into most feasible structures formed in experiments, thereby providing an estimate of the corresponding 6F-CMSM density. Using grand canonical Monte Carlo simulations, we observe that high isosteric heats of adsorption for CO 2 leads to enhanced adsorption capacity and high sorption selectivity from binary mixtures of these gases. Studying the asphericity of polymer chains, we report the existence of an optimum chain length of highest curvature, leading to low density, high porosity, and high CO 2 adsorption capacities that compare well with available experimental data, without compromising sorption selectivity of 6F-CMSM. This work provides a theoretical basis of how slight modifications of the physical arrangements of chemical components lead to significant changes in porosity and gas adsorption capacities of molecular sieving membranes.