Covering the conical nanochannels with dense polyelectrolyte layers significantly improves the ionic current rectification.

Because of their asymmetry, conical nanochannels/nanopores exhibit various attractive electrokinetic features, including ion selectivity, ionic concentration polarization, and ionic current rectification. The polyelectrolyte layer (PEL)-covered (soft) conical nanochannels have recently attracted significant attention because of their unique rectification characteristics. In the modeling of soft nanochannels, it is usually assumed that the properties of the PEL and the electrolyte are the same, an assumption that is not true, especially for dense PELs. In the present work, the influence of the PEL-electrolyte property difference on the ionic current rectification in conical soft nanochannels is studied. To this end, adopting a finite-element approach, the Poisson-Nernst-Planck and Navier-Stokes equations are numerically solved for a steady-state by considering different values of permittivity, diffusivity, and dynamic viscosity for the PEL and the electrolyte. The model is validated by comparing the results with the available theoretical and experimental data. The results show that the PEL-electrolyte property difference leads to a significant improvement of the rectification behavior, especially at low and moderate salt concentrations. This not only highlights the importance of considering different properties for the PEL and the electrolyte but also implies that the rectification behavior of soft nanochannels/nanopores may be improved considerably by utilizing denser PELs.