Salt Ion Transport Through Carbon Nanotubes: Insights from Polarizable Force Field-Based Molecular Dynamics Simulations

Carbon Nanotubes (CNTs) which are cylindrical 1D allotropes of carbon are emerging as promising materials for membrane-based applications, including seawater desalination and osmotic power harvesting. For the rational design of CNTs in membrane-based applications, it is imperative to develop a fundamental understanding of the interactions of salt ions such as Na⁺ and Cl^- with the carbon atoms of CNTs. Given the large polarizability tensors of CNTs, salt ions inside CNTs can exert strong electric fields which can result in a significant polarization of the CNTs. Although the ion – CNT polarization energy is high (e.g., 27 kcal/mol inside a 0.8 nm diameter CNT) and makes the dominant contribution to the ion - CNT binding energy, previous MD simulation studies have neglected the polarization of CNTs in the presence of water molecules and salt ions. In this talk, we discuss our formulation of polarizable force fields parameterized using quantum chemical simulations which can self-consistently model the anisotropic polarizability tensors of CNTs, as well as reliably model water-CNT and ion-CNT interactions. Finally, by performing classical MD simulations with polarizable force fields, we carry out a comprehensive investigation of salt ion transport through 0.8 – 2 nm diameter CNTs.