(185g) Ion Transport in Charged Nanopores

The spatial distribution and transport of ions through charged nanopores is fundamental to existing and emerging technologies for ionic separations, electrochemical storage, and energy harvesting. In strong confinement in nanopores, the electrical double layers from bounding pore walls can overlap, leading to charge exclusion and surface-dominated conductance. As concentrated electrolytes are confined in pores of molecular dimension, classical theories fail to describe the ionic distributions and transport behavior. Here, we develop mathematical frameworks to analyze the physics of overlapping double layers, and how electrostatic correlations and excluded volume effects change the double layer structure, thermodynamic properties, and force-flux relationships for transport. At high surface charge density or for multivalent ions, attractive electrostatic forces arise between two like-charged surfaces due to strong ion-ion correlations. For sufficiently large ionic concentrations, over-screening of surface charges leads to charge density oscillations, changing the electrosorption behavior of interfaces. We show that dimensionality of confinement affects the charge screening properties, and that electrolytes confined to one-dimension exhibit exponentially long screening lengths. In fact, for sufficiently small nanopores, we predict the occurrence of electroneutrality breakdown over macroscopic length scales, where the number of charges on the pore walls is not balanced by ionic countercharges within the pore. Finally, we extend the analysis to multipore arrays, where we find that pore-pore interactions governed by geometric length scales determine the conductance and selectivity of an ensemble of neighboring pores. The electrokinetic couplings of ion transport, electrostatics, and fluid flow are implemented in these regimes to optimize transport, selectivity, and electrokinetic conversion efficiencies.