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