(253aw) Molecular Dynamics Simulation of Water and Ion Transport through Carbon Nanotubes

Authors: 
Aranha, M., The University of Tennessee
Edwards, B. J., University of Tennessee

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.