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.
Article: Water infiltration behaviours in carbon nanotubes under quasi-static and dynamic loading conditions[show abstract] [hide abstract]
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.
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ABSTRACT: Water molecules confined to nonpolar pores and cavities of nanoscopic dimensions exhibit highly unusual properties. Water filling is strongly cooperative, with the possible coexistence of filled and empty states and sensitivity to small perturbations of the pore polarity and solvent conditions. Confined water molecules form tightly hydrogen-bonded wires or clusters. The weak attractions to the confining wall, combined with strong interactions between water molecules, permit exceptionally rapid water flow, exceeding expectations from macroscopic hydrodynamics by several orders of magnitude. The proton mobility along 1D water wires also substantially exceeds that in the bulk. Proteins appear to exploit these unusual properties of confined water in their biological function (e.g., to ensure rapid water flow in aquaporins or to gate proton flow in proton pumps and enzymes). The unusual properties of water in nonpolar confinement are also relevant to the design of novel nanofluidic and molecular separation devices or fuel cells.Annual Review of Physical Chemistry 02/2008; 59:713-40. · 14.13 Impact Factor