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: The mechanisms of pressure-driven water infiltration into single walled carbon nanotubes are explored using molecular dynamics simulations. Both quasi-static and dynamic loading conditions are investigated, and the influence of tube size is examined. Under quasi-static loading, the water molecules flow into the tube via surface diffusion at a low pressure and when the external pressure reaches a critical value, the infiltrated water flux can sharply increase to a steady state. Upon dynamic loading, the nominal infiltration length per unit external work is employed to measure the comprehensive effect of the loading rate. It is found that such factor is larger (i.e. infiltration is easier) at a lower loading rate and a larger tube size, which is closely related with the interactions between water molecules and nanotube wall atoms.Molecular Simulation 09/2008; 34. DOI:10.1080/08927020802175225 · 1.12 Impact Factor
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ABSTRACT: Proton transfer and transport in water, gramicidin and some selected channels and bioenergetic proteins are reviewed. An attempt is made to draw some conclusions about how Nature designs long distance, proton transport functionality. The prevalence of water rather than amino acid hydrogen bonded chains is noted, and the possible benefits of waters as the major component are discussed qualitatively.Biochimica et Biophysica Acta 09/2006; 1757(8):886-912. DOI:10.1016/j.bbabio.2006.06.017 · 4.66 Impact Factor
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ABSTRACT: The geometry structures and vibrational infrared and resonant Raman spectra of ordered n-gonal water nanotubes, n = 5-7, were systematically studied using a self-consistent charge density-functional tight-binding method complemented with an empirical van der Waals force correction. It is shown that water molecules can form cylindrical crystalline structures, referred to as ice nanotubes, by hydrogen bonding under confinement within single-walled carbon nanotubes. The hydrogen bond plays an important role not only in formation of the unique structures of ice nanotubes but also in the signatures in their vibrational spectra. The calculated infrared spectra in the low-frequency domain show a series of weak bands involving hydrogen bonds along with two librational bands which arise from the constraints induced by hydrogen bonding. In the middle-to-high-frequency region, the intramolecular bending bands of ice nanotubes are shifted to lower frequencies with regard to those of conventional hexagonal ice phase, whereas the intramolecular symmetric and asymmetric stretching bands are shifted to higher frequencies as the hydrogen-bond networks of ice nanotubes are weaker than those of conventional hexagonal ice. The predicted resonant Raman spectra also present distinctive features between those ice nanotubes.The Journal of Physical Chemistry C 09/2007; 111(38). DOI:10.1021/jp0742822 · 4.84 Impact Factor