Diode-like response of conical-shaped nanochannels to external stimuli: The importance of slip length

Abstract

The present study reports the effect of slip length on the ionic current rectification and ion selectivity in conical-shaped electrolyte-loaded nanochannels with and without a coated polyelectrolyte layer (PEL). The electrolyte was considered a salted incompressible Newtonian fluid. The polyelectrolyte layer was also modeled as a rigid and charged porous solid saturated with a salted Newtonian fluid. The electrolyte-polyelectrolyte layer interface was modeled as a surface, considering ion partitioning with distinct physical properties across the interface. The results demonstrated that the relationship between the slip length and the rectification factor depended on the surface charge density, the concentration of the electrolyte solution, and the type of nanochannel. Moreover, the effect of slip length on the ion selectivity factor is remarkably higher in the solid-state nanochannel compared to the PEL-coated nanochannel. Furthermore, the slip length considerably enhances the ion selectivity factor in the solid-state nanochannel. Considering a bulk concentration of 100 mM, a charge density of 60 mol m−3, and a surface charge density of −20 mC m−2, the ionic rectification factor was degraded by 49% and enhanced by 43%, respectively, for the solid-state and PEL-coated nanochannels when the slip length is taken into account.