Exploration of gas molecules transport in composite poly (4-methyl-2-pentyne) and carbon nanotubes employing molecular dynamics simulation

• Published in: Computational materials science Vol. 143; pp. 87 - 94
• Main Authors: Yang, Quan, Achenie, Luke E.K.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.02.2018
• Subjects: Carbon nanotubes; Composite; Molecular dynamics method; Composite; Carbon nanotubes; Molecular dynamics method
• ISSN: 0927-0256; 1879-0801
• DOI: 10.1016/j.commatsci.2017.10.050

[Display omitted] •It is essential to study penetrant transport in PMPCNT from molecular level viewpoints.•The complicated structures of PMPCNT were established successfully and then relaxed.•The ballistic regime in PMDPCNTC is shorter than in PMDPCNTO.•In PMPCNTC, the 25 positions that contribute most to solubilities are outside the carbon nanotubes, while in PMPCNTO, they are inside.•The selectivity of n-C4H10 over CH4 is 22 in PMPCNTO, and 41 in PMPCNTC. In order to design optimal membrane composites it is important to have an in-depth understanding of penetrants transport in such membranes. In that spirit, molecular dynamics was employed to study the transport of gas molecules in a composite membrane consisting of poly (4-methyl-2-pentyne) (PMP) and close-ended carbon nanotubes (PMPCNTC) or open-ended carbon nanotubes (PMPCNTO). The logarithm plot of mean-squared displacement (MSD) versus time for the transport of methane in PMPCNTC and PMPCNTO was drawn. It is observed that there are three regimes: the ballistic regime, the subdiffusive regime and the Fickian diffusive regime. The ballistic regime in PMPCNTC is shorter than it is in PMPCNTO, because the average cavity size of PMPCNTC is smaller than that of PMPCNTO and the penetrants have more space to move freely in PMPCNTO than they do in PMPCNTC before they hit any matrix units. Then the diffusivities of penetrants were achieved according to the plot of MSD versus time for the transport of penetrants in the Fickian diffusive regime. The solubility coefficients and the permeability of gas molecules in the composites were also calculated. In PMPCNTC, the 25 locations that contribute most to solubilities are outside the nanotubes while in PMPCNTO, they are inside the nanotubes. In PMPCNTO it is the nanotube that solvates the majority of the gas molecules. The huge channels inside the nanotube cause the high solubility of these penetrants. Finally, the selectivity of n-C4H10 over CH4 in PMPCNTC is observed to be higher than it is in both PMPCNTO and pure PMP. The research results may be employed in membrane design.