Anomalous ion transport through angstrom-scale pores: Effect of hydration shell exchange on ion mobility

Abstract

In this work, the ion transport of K+ and Li+ through angstrom-scale pores was thoroughly investigated using molecular dynamics (MD) simulation. Despite of their similar sizes, anomalously selective behaviors were observed. Our MD simulations found that the selectivities through two kinds of pores with diameters of 4 Å and 5 Å show an opposite preference on K+ or Li+ respectively under certain applied voltage. We demonstrated that the exchange of hydration shell with surrounding water molecules plays an important role in the ion mobility. Higher exchange rate equivalently reduces the apparent friction of the hydrated ion during its migration, thus increases the ion mobility. The interactions between ions and the pore edge also contribute to the ion mobility. Our results provide insights into the atomic scale details of ion transport process. Based on these findings, the applied voltage and pore size can be used to actively control the selectivity of K+/Li+ ions.