Water flow in a cylindrical nanopore with an object

Abstract

Understanding the physics of water movement through a nanopore with an object is critical for better control of water flow and object translocation. It should help in the design of nanopores as molecular and viral sensors. We evaluated how the external electric field and ion concentrations, pore wall charge density, disk radius and charge density, and ion mobility influence the water flow in a charged cylindrical nanopore using Poisson–Nernst–Planck–Navier–Stokes simulations. We dissected water flow induced by the external electric field (“external” component) from that generated by the field induced by the fixed and mobile charges (“charge” component). The velocity and direction of the axial flow “external” component were controlled directly by the external electric field. The pore wall charges also influenced them indirectly by altering the density and distribution of mobile charges. Higher external concentrations enhanced the axial water flow by lowering its charge component. The ion mobility and disk charge slightly influenced the axial water flow. The axial body forces near the wall drive the axial water flow near the pore wall. If the disk is large, water also flows axially in the opposite direction near the pore center. Local forces near the disk do not control the radial water flow near the disk. The axial body force and water flow near the pore wall do. If an annulus replaces a disk, the axial forces near the pore wall control the radial flow near the annulus and the axial flow within its hole.