Bipolar nanochannels: a systematic approach to asymmetric problems *

Nanofluidic diodes are capable of rectifying the electrical current by orders of magnitude. In the current state of affairs, determining the rectification factor is not possible as it depends on many system parameters. In this talk, we will show how an interplay of geometric and surface charge effects can vary the current−voltage response between the two extreme behaviors of unipolar and bipolar responses. To this end, we account for the diode and its adjacent microchannels whereby we vary both the geometry and the surface charge to any desired configuration. Instead of the classical signature of concentration polarization, such as ionic depletion and enrichment, our system exhibits a more complicated behavior as such the formation of two depletion layers. The system can be characterized by various steady-state parameters such as the transport numbers and rectification factor, but we also show that these “steady-state” parameters exhibit spatial and temporal dependencies. The findings of our work [1] can be used to elucidate the complicated behavior of ion transport in nanofluidic diodes and to rationalize experimental results. The insights of this work can be used to improve the design of nanofluidic diodes.

[1] Abu-Rjal and Green, ACS Appl. Mater. Interfaces 13, 27622 (2021).