How SWCNT Chirality Governs Gas Transport and Selectivity in Aligned PA–6,6 Membranes: A Molecular Dynamics Study

ABSTRACT This study presents a molecular dynamics investigation of CH 4 , CO 2 , and CO transport through aligned single‐walled carbon nanotubes (SWCNTs) embedded within a polyamide–6,6 (PA–6,6) matrix. SWCNTs with nearly identical diameters and lengths but different chiral indices were systematically examined to isolate the specific role of chirality in governing gas adsorption, diffusion, permeability, and selectivity. The surrounding PA–6,6 matrix acts as a structural barrier, restricting molecular transport exclusively to the inner nanotube channels. The results reveal that gas diffusion coefficients follow the order CO > CH 4 > CO 2 , whereas adsorption strength follows the reverse trend, with CO 2 exhibiting the strongest interaction with the CNT walls. Within the solution–diffusion framework, the enhanced adsorption of CO 2 compensates for its lower mobility, resulting in an overall permeability trend of CO > CO 2 > CH 4 across all investigated systems. Carbon monoxide exhibits exceptionally high permeation rates, reaching 134.85 nm − 1 s − 1 bar − 1 in the SWCNT (14,0) structure. Ideal selectivity analysis demonstrates a strong separation preference for CO over CH 4 and CO 2 , while CO 2 /CH 4 selectivity remains near unity. These findings highlight chirality as a critical parameter for tuning nanoscale gas transport in PA–6,6/SWCNT composite membranes.

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