Molecular Dynamics Simulation of Water and Ion Transport through Carbon Nanotubes

Carbon nanotubes possess smooth hydrophobic surfaces and can be chemically functionalized enabling advanced separation processes by permitting high water flow rates while efficiently partitioning ions. Application of continuum theories to describe transport of water and ions may become difficult at the nanoscale and thus alternate techniques that help to evaluate structural and dynamical features in atomic detail such as molecular dynamics simulations are often used. We present our results from molecular dynamics simulations of pure water with two different water models (SPC/E and TIP4P/2005) and a 1:1 aqueous solution of NaCl confined in sub-3 nm diameter finite carbon nanotubes. The equilibrium density profiles of water and ions in these narrow pores are shown and their correlations with the observed dynamic properties in terms of diffusion coefficients obtained via the Einstein equation and the Green-Kubo relation are discussed. The transport properties are further evaluated by calculation of the permeation events of water and ions through charged and uncharged nanotubes. Additionally, we also obtain measurements of ion occupancy in the nanotube, hydration numbers of ions, water and ion fluxes, and ion rejection rates. The role of confinement and charge on the physical features of water and ion transport through carbon nanotubes obtained via MD simulation will be presented in this poster.