Fine-tuning ionic transport through hybrid soft nanochannels: The role of polyelectrolyte charge density distribution

Abstract

This study investigates a hybrid nanochannel consisting of two cylindrical and conical parts coated with a soft layer exhibiting either of four different spatial distribution functions: constant (type I), exponential (type II), sigmoidal (type III), and soft-step (type IV). The Poisson–Nernst–Planck and Navier–Stokes equations are numerically solved using the finite element method under steady-state conditions. The research focuses on the modification of behavior and enhancement of performance in nanochannels inspired by nature. Considering the spatial variation in charge density distribution and the limited understanding of ion transport mechanisms, this study highlights the importance of modeling tools in advancing this field. The findings contribute to the development of effective strategies for controlling and manipulating the behavior of charged nanochannels. The results demonstrate that changing the decay length from 0.2 to 1 at a concentration of 1 mM leads to an increase in the rectification factor for type II up to 6.129, i.e., 5.7 times. Furthermore, varying NPEL/NA from 25 to 100 mol m−3 at Vapp=+1 V results in ionic selectivity of 0.9072, 0.2009, 0.1543, and 0.9031 for functions of type I to type IV, respectively. These findings not only enhance our understanding of ion transport mechanisms in hybrid nanochannels but also suggest that manipulating the charge density of the soft layer enables the production of intelligent nanochannels with applications in separation, diagnostics, and sensing.