Curious Characteristics of Polar and Nonpolar Molecules Confined within Carbon Nanotubes (CNT) of Varied Diameter: Insights from Molecular Dynamics Simulation

P Sahu and SM Ali, JOURNAL OF CHEMICAL AND ENGINEERING DATA, 62, 2307-2315 (2017).

DOI: 10.1021/acs.jced.7b00186

Carbon nanotube (CNT) has emerged as a potential candidate for desalination of salty water as well as for purification of various kinds of gaseous and liquid mixtures which is controlled by the interaction of the fluid molecules within the nanocavity of CNT. It is, therefore, worthwhile to investigate the behavior of both the polar and nonpolar fluid molecules within the nanoconfinement of CNT at the molecular level. In the present study, molecular dynamics simulations have been performed to investigate the structure and dynamics of polar and nonpolar molecules within CNTs. Results show the enhancement of confined density with increase in nanotube diameter. Single file flow of water, methanol, and methane inside CNT(6,6) was diminished with increase in nanotube diameter and converted to layered flow for larger CNTs. Surprisingly, results showed controversial effects of nanotube dimension for dynamics of polar and nonpolar fluids, which has been explained in terms of interaction forces acting between fluid particles and fluid nanotube wall. The density of states (DOS) results have been found in line with the corresponding velocity autocorrelation function (VACF). Interestingly, the altered H bonding of methanol in the axial and radial direction of CNT(6,6) and CNT(7,7) conceded the reversal effects on rotation degree of freedom (DOF) and translation DOF respectively. However, all such effects were observed to be vanished for the larger diameter of CNTs. Overall, the present study provides an insightful view of flow transition from sub continuum to bulk fluid properties, while moving from small to large diameter CNTs, established with both the polar and nonpolar fluids, which is supposed to be very supportive for understanding of equivalent fluid channels in living cells, and the CNTs would serve as good prototypes for narrow biological channels.

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