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Unformatted text preview: Fluid structure and transport properties of water inside carbon nanotubes Yingchun Liu, Qi Wang, a ! Tao Wu, and Li Zhang Department of Chemistry, Zhejiang University, Hangzhou 310027, People’s Republic of China s Received 13 July 2005; accepted 6 October 2005; published online 19 December 2005 d The fluid structure and transport properties of water confined in single-walled carbon nanotubes s CNTs d with different diameters have been investigated by molecular-dynamics simulation. The effects of CNT diameter, density of water, and temperature on the molecular distributions and transport behaviors of water were analyzed. It is interesting that the water molecules ordered in helix inside the s 10, 10 d CNT, and the layered distribution was clearly observed. It was found that the axial and radial diffusivities in CNTs were much lower than that of the bulk, and it ever decreased as the diameter of CNT decreases. The axial thermal conductivity and shear viscosity in CNTs are obviously larger than that of the bulk and those in the radial direction, they increase sharply as the diameter of CNT decreases, which is clearly in contrast to the diffusivity. The inner space of CNT and the interactions between water molecules and the confining walls play a key role in the structure and transport properties of water confined in the CNTs. © 2005 American Institute of Physics . f DOI: 10.1063/1.2131070 g I. INTRODUCTION Single-walled carbon nanotubes s CNTs d have many po- tential applications, such as molecular sieves, membranes, sensors, nanofluidic devices, and “nanopipes” for the precise delivery of gases or liquids. 1–3 They also provide an ideal model system for investigating the microscopic details of fluid transport in very small pores. There have been several studies of dynamic molecular flow, 4–6 diffusive molecular flow, 7–10 and molecular adsorption 11,12 in CNTs. For ex- ample, Fan et al. 6 found the ordered atomic arrangement of iodine atoms in the form of helical chains inside CNTs by Z-contrast scanning transmission microscopy images, and a consistent interpretation of the experimental data was pro- vided by density-functional theory calculations and topologi- cal considerations. Mao and Sinnott 8,9 have investigated the diffusive behavior of ethane and ethylene in CNTs using classical molecular-dynamics s MD d simulations and density- functional theory calculations. They found that at low mo- lecular densities, these nonspherical molecules follow a spi- ral path inside CNTs with diameters of 13–22 Å. Also, Cao and Zu 10 calculated the diffusivities of methane in CNTs. It was found that the parallel self-diffusion coefficient of meth- ane in an infinitely long and at subcritical temperatures, the diffusion of methane in a fully loaded CNT follows a solid- like behavior, varies drastically with the nanotube diameter....
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