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.
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ABSTRACT: On the basis of realistic tight-binding band-structure calculations, we predict that carbon microtubules exhibit striking variations in electronic transport, from metallic to semiconducting with narrow and moderate band gaps, depending on the diameter of the tubule and on the degree of helical arrangement of the carbon hexagons. The origin of this drastic variation in the band structure is explained in terms of the two-dimensional band structure of graphite.Physical Review Letters 04/1992; 68(10):1579-1581. · 7.94 Impact Factor
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ABSTRACT: Dynamic properties of supercritical water at temperatures between 573 and 773 K and densities between 0.49 and 0.83 g/cm(3) have been investigated by molecular dynamics simulation and compared to states located on the vapor-liquid coexistence curve. A flexible simple point charge potential has been assumed for interactions in the subcritical states, whereas a reparameterization of that model has been performed to model the supercritical states. The hydrogen bonding structure and the diffusion coefficients in an ensemble of simulated states were previously analyzed and a good agreement with available experimental data was found. Dynamic properties of hydrogen bonding like the bond lifetimes and the influence of hydrogen bonds in the vibrational spectra are discussed along a range of simulation conditions. A nonlinear behavior of the hydrogen-bond lifetime as a function of temperature is observed in subcritical water whereas a linear dependence is found in supercritical water. Special attention is paid to the intermolecular vibrational spectrum (10-400 cm(-1)). It has been observed that the mode centered at 200 cm(-1), attributed to the intermolecular O-O stretching vibration in the ambient state remains active in the supercritical states.Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics 02/2000; 61(1):449-56.