(Invited) Electroosmotic Flow-Driven Ion Current Rectification and Negative Differential Electrolyte Resistance in Nanofluidics

Abstract

Ion current rectification (ICR) refers to an asymmetric diode-like current-voltage behavior when switching the polarity of applied voltage bias on a nanopore, and negative differential resistance (NDR) refers to a negative conductance behavior, that is, the current decreases with increasing applied voltage bias. Previous studies have shown that the former can be found in a charged nanopore, which has at least one side with dimension comparable to its electric double layer; therefore, the symmetry of ionic concentrations across a nanopore can be broken. The latter can also be achieved in a charged nanopore, which is filled with an aqueous solution with higher salt conductivity and an organic solution with lower salt conductivity, by the competition between the electroosmotic flow (EOF) and the pressure-driven flow. In this talk, I will show the first experimental result that both the ICR and NDR phenomena can be observed in a charged nanopore without conventional rigorous conditions such as overlapped electric double layer, external pressure, and organic solutions. Results show that both the ICR and NDR phenomena depend highly on the solution pH and solution properties. In addition to experimental observations, the model comprising the coupled Poisson-Nernst-Planck (PNP) and Navier-Stokes (NS) equations are employed to demonstrate that both the ICR and NDR phenomena results mainly from the EOF-driven mechanism.