Temperature effects on the static and dynamic properties of liquid water inside nanotubes

Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, B5 Campus Nord, 08034 Barcelona, Catalonia, Spain.
Physical Review E (Impact Factor: 2.29). 09/2001; 64(2 Pt 1):021504. DOI: 10.1103/PhysRevE.64.021504
Source: PubMed


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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    • "Therefore, in order to understand the above experimental results, theoretical and numerical studies are necessary. Molecular dynamics (MD) simulations have been carried out for studying the transport behaviours of molecules inside CNTs [13] [14] [15] [16] [17]. For instance, Hummer et al. [18] immersed a very short (6,6) CNT (with the length of about 1.3 nm and with both ends open) in a reservoir with 1000 water molecules, and reported that such an initially empty SWCNT can be filled instantaneously by surrounding water molecules under ambient conditions. "
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    • "However, the wall interactions in a polar pore are not negligible, as they appear to be in a hydrophobic pore. Simulations on carbon nanotubes [100] and hydrophobic pores [93] [96] show that as the diameter of the pore is decreased below 20 Å, the average density of water decreases due to increasing frequency of transition to the vapor phase. At the same time, the diffusion coefficient increases—by as much as 3-fold in the narrowest channels to have significant water density. "
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