Molecular Dynamics Study on Diameter Effect in Structure of Ethanol Molecules Confined in Single-Walled Carbon Nanotubes

Abstract

Equilibrium molecular dynamics simulations have been performed to investigate the structural characteristics of ethanol molecules confined in single-walled, pristine armchair carbon nanotubes with a length of 2.5 nm and diameters ranging from 0.68 to 1.35 nm in an open ethanol reservoir at 298.0 K and 100.0 kPa by all-atom and united-atom models. Both models present similar results. Structural properties of confined ethanol molecules are analyzed in terms of the average number of hydrogen bonds, radial density distributions of methyl and hydroxyl groups, orientation distributions of the methyl-methylene bond, oxygen-hydrogen bond and dipole moment, and molecular conformations as a function of the diameter of carbon nanotubes. The results indicate that the behavior of the nonpolar part of confined ethanol molecules changes monotonically with the diameter, whereas that of the polar part changes non-monotonically. The different dependence on diameter indicates that the wall-fluid interactions determine the behavior of nonpolar groups, whereas that of polar groups is determined by the fluid-fluid interactions. Only in the nanotube with a diameter of 1.081 nm did the confined ethanol molecules have a highly preferred dipole orientation. The conformational equilibrium also varies considerably with the diameter non-monotonically. The largest proportion of gauche ethanol corresponds to the most preferred dipole orientation.

Tuning the energy barrier of water exchange reactions on Al(iii) by interaction with the single-walled carbon nanotubes

“…However, the average Al-O bond length inside (13,0) is 1.931 A ˚, much smaller than that in the isolated system, indicating that the confinement effect of the carbon nanotube is remarkable in the D pathway inside (13,0) system. This point is consistent with the findings of Shao et al 21 and Kaczmarek et al 22 It is noticeable that the average Al-O bond length inside (14,0) is 1.939 A ˚, much larger than that inside (13,0), and close to that in the isolated system, indicating that the confinement effect of the carbon nanotube decreases rapidly along with the increasing of diameter of the carbon nanotube. Comparing the structural parameters for the transition states, especially Al-O L distance in the transition state, the influences of (13,0) and (14,0) on transition states are Fig.…”

Alcohol-induced drying of carbon nanotubes and its implications for alcohol/water separation: A molecular dynamics study

“…Here, the numbers of organic and water molecules in the given simulation boxes were calculated according to the experimentally determined partial molar volumes of organic molecules (at a concentration of 1 M) 32 and water 33 at 298 K. We used the TIP3P water model, 34 and OPLSAA force field 35 which was commonly used for simulations of organic molecules especially linear alcohols. 16,29,36,37 Second, the energies of the binary solution systems were minimized with a steepest descent algorithm, followed by a 1ns NPT equilibration at 298 K. Third, the SWNT was inserted in the equilibrated binary solution, with water/organic molecules removed if the distance between oxygen of water and any carbon atom of SWNT was <2.7 Å, or if the distance between any heavy atom of alcohols/phenol and any carbon atom of SWNT was <2.4 Å. 38 The resulting concentrations of aqueous solutions are also roughly 1 M, with the number of organic and water molecules for different production simulations summarized in Table I.…”

“…The carbon nanotubes possess well-defined hollow structures and, thus, serve as desirable materials for molecules adsorbing into their interiors. [14][15][16][17][18][19] Recently, it has been proposed that the SWNTs (or SWNT bundles/membranes) can be used to separate water from salt solution, 20 separate binary mixture of organic a) Authors to whom correspondence should be addressed. Electronic addresses: xiupeng2011@zju.edu.cn and ystu@shu.edu.cn.…”

Molecular dynamics study of dipalmitoylphosphatidylcholine lipid layer self-assembly onto a single-walled carbon nanotube

“…The time step size was 2 fs. Based on previous work, the SWNT atoms were modeled as uncharged Lennard-Jones particles using sp 2 carbon parameters [23,24] with a cross section of CC = 0.365 nm, and a depth of the potential well of CC = 0.465 kJ/mol. For the DPPC molecule, we used Berger's parameters [25].…”