Atomic Scale Design and Three-Dimensional Simulation of Ionic Diffusive Nanofluidic Channels

Recent advance in nanotechnology has led to rapid advances in nanofluidics, which has been established as areliable means for a wide variety of applications, including molecular separation, detection, crystallization andbiosynthesis. Although atomic and molecular level consideration is a key ingredient in experimental design andfabrication of nanfluidic systems, atomic and molecular modeling of nanofluidics is rare and most simulationsat nanoscale are restricted to oneor two-dimensions in the literature, to our best knowledge. The present workintroduces atomic scale design and three-dimensional (3D) simulation of ionic diffusive nanofluidic systems. Wepropose a variational multiscale framework to represent the nanochannel in discrete atomic and/or moleculardetail while describe the ionic solution by continuum. Apart from the major electrostatic and entropic effects,the non-electrostatic interactions between the channel and solution, and among solvent molecules are accountedin our modeling. We derive generalized Poisson-Nernst-Planck (PNP) equations for nanofluidic systems.Mathematical algorithms, such as Dirichlet to Neumann mapping and the matched interface and boundary(MIB) methods are developed to rigorously solve the aforementioned equations to the second-order accuracyin 3D realistic settings. Three ionic diffusive nanofluidic systems, including a negatively charged nanochannel,a bipolar nanochannel and a double-well nanochannel are designed to investigate the impact of atomic chargesto channel current, density distribution and electrostatic potential. Numerical findings, such as gating, iondepletion and inversion, are in good agreements with those from experimental measurements and numericalsimulations in the literature.