Design of Copolymers for CO₂/N₂ Separation Membranes: Insights From Molecular Simulations and Experiments

Copolymers containing polyethylene oxide (PEO) have shown remarkable potential for CO 2 separation. Here, we combine full atomistic simulations with experimental measurements to systematically investigate the influence of PEO molecular weight on CO 2 /N 2 transport in polyethylene oxide–block–polybutylene terephthalate (PEOT‐b‐PBT) membranes. The simulated density of the PBT segment closely matches experimental observations, confirming the reliability of our model. We provide molecular‐level insights into membrane microstructure by comprehensively analyzing cohesive energy density, solubility parameters, chain mobility, fractional free volume, and pore size distribution. The results reveal a competitive affinity for CO 2 , leading to enhanced solubility and diffusivity selectivity—particularly in lower‐molecular‐weight PEO segments—with solubility emerging as the dominant factor for CO 2 /N 2 separation. Among the investigated samples, 1000 and 2000 EB exhibited the highest CO 2 /N 2 permselectivity, whereas 8000 and 10,000 EB displayed the greatest CO 2 permeability. The strong agreement between experimental findings and computational predictions underscores the robustness of this approach for elucidating gas transport behavior in PEOT‐b‐PBT membranes.