Molecular Dynamics Simulations of Ion Transport in Carbon Nanotube Channels

We present a computational modeling study examining ion transport dynamics of aqueous electrolytes under severely confined conditions. Ionic current and solvent transport through carbon nanotubes in an external electric field are studied using all atom molecular dynamics simulations. Specifically, we have examined the behavior of sodium and chloride ions in nanotubes of different radii to assess the influence of confinement on the ionic current. We find a linear relationship between the current computed and potential applied for the wider nanotubes; however, there is a significant departure from linearity when the tube diameter becomes comparable to the size of the solvated ion. For the smallest tubes studied, the energy penalty to access the pore interior is too great for most ions, leading to minimal current. We provide analyses of the energy barriers associated with ion entry as well as the hydration shell properties, which supports the absence of ionic current in the smallest carbon nanotubes.