Transport behavior of water confined in carbon nanotubes

The transport properties of water confined in single-walled carbon nanotubes with diameters from 1.1 nm to 2.1 nm were investigated by molecular dynamics simulations. It was found that the transport properties are anisotropic, the axial diffusivity, thermal conductivity, and viscosity are much larger than those in the radial direction. The diffusivity in carbon nanotubes is obviously lower than that of the bulk and it decreases as the diameter of the nanotube decreases. Particularly contrary to the diffusivity, the axial thermal conductivity and shear viscosity in carbon nanotubes is much higher than those of the bulk, and it increases sharply as the diameter of the nanotube decreases. The water molecules ordered in helix inside the (10, 10) single-walled carbon nanotube (SWCN) and the layered distribution was clearly observed.

Figure 1

The diffusivity and its components of water inside the SWCNs as a function of diameter of nanotubes at 298 K, $1.0\mathrm{g}{\mathrm{cm}}^{-3}$.

Figure 2

The thermal conductivity and its components of water inside the SWCNs (the contribution of the SWCN itself was not included) as a function of diameter of nanotubes at 298 K, $1.0\mathrm{g}{\mathrm{cm}}^{-3}$.

Figure 3

The shear viscosity and its components of water inside the SWCNs as a function of diameter of nanotubes at 298 K, $1.0\mathrm{g}{\mathrm{cm}}^{-3}$.

Figure 4

(Color) A snapshot of the distribution of water molecules confined in (10, 10) SWCN at 298 K, $1.0\mathrm{g}{\mathrm{cm}}^{-3}$. The water molecules ordered in helix are clearly observable.