Temperature effects on the static and dynamic properties of liquid water inside nanotubes.
ABSTRACT We report a molecular dynamics simulation study of the behavior of liquid water adsorbed in carbon nanotubes under different thermodynamic conditions. A flexible simple point charged potential has been employed to model internal and intermolecular water interactions. Water-carbon forces are modeled with a Lennard-Jones-type potential. We have studied three types of tubes with effective radii ranging from 4.1 to 6.8 A and three temperatures, from 298 to 500 K for a fixed density of 1 g/cm(3). Structure of each thermodynamic state is analyzed through the characterization of the hydrogen-bond network. Time-dependent properties such as the diffusive behavior and molecular vibrational spectra are also considered. We observe the gradual destruction of the hydrogen-bond network together with faster diffusive regimes as temperature increases. A vibrational mode absent in bulk unconstrained water appears in the power spectra obtained from hydrogen velocity autocorrelation functions for all thermodynamic states. That frequency mode should be attributed to confinement effects.
- [Show abstract] [Hide abstract]
ABSTRACT: Single-walled carbon nanotubes (SWCNTs) are seamless cylindrical tubes consisting of carbon atoms with diameters ranging from less than one nanometer to a few nanometers. The arrangement of carbon atoms in a SWCNT is uniquely specified by using a pair of integers (n, m) referred to as the chiral indices. While the detailed structures, such as a carbon–carbon bond length, should be important, they have not been fully clarified yet. In this work, we examine the possibility of powder X-ray diffraction (XRD) method to characterize structures of SWCNTs. It is found that the XRD is a useful tool to “fingerprint” the chiral indices of bulk SWCNT samples. Besides, we find that information on the detailed structure within a SWCNT can be obtained from the XRD pattern. The application to a highly concentrated SWCNTs clarifies that the (6,5) SWCNT is expanded along the radial direction compared to that of ideal rolling up structure of graphene, with a negligible change along the tube axis.Carbon 08/2014; 75:299–306. · 6.16 Impact Factor
Article: Biophysics: Water at the nanoscaleNature 01/2001; 414:156-159. · 42.35 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: This study utilizes molecular dynamics simulation to investigate the behavior of water molecules inside Au nanotubes of various sizes. An observation of the water molecule distributions reveals that the adsorption of the water molecules creates two shell-like formations of water in close vicinity to the Au nanotube wall and these shell-like formations are found to be more pronounced in nanotubes of smaller diameter than in larger nanotubes. In smaller Au nanotubes, the higher concentration of water molecules in close vicinity to the wall lowers the density of the water molecules in the random distribution region and reduces the number of hydrogen bonds between a water molecule and its neighboring water molecules. These results can be attributed to the increase in the average interaction energy between the Au nanotube and the water molecules as the size of the nanotube decreases. Finally, an inspection of the variation in the self-diffusion coefficients of the water molecules in the random distribution region of the Au nanotube reveals that water molecules in a smaller Au nanotube have a greater ability to diffuse along the longitudinal direction of the nanotube.Microporous and Mesoporous Materials 10/2004; 75(1):81-87. · 3.21 Impact Factor