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.

Ion Transport in Intelligent Nanochannels: A Comparative Analysis of the Role of Electric Field

“…Remarkably, across the spectrum of examined nanochannels, characterized by C 0 = 20 mM, a distinctive feature emerges: the degree of ionic concentration polarization (ICP) is conspicuously prominent. , This observation holds true for both conical and cylindrical nanochannels, with the former exhibiting an ICP notably higher than that of the latter. The rationale behind this divergence can be ascribed to the geometric disparity; specifically, the asymmetric nature of conical nanochannels leads to an amplified EDL overlap at the tip area, a phenomenon exceeding that observed in symmetric cylindrical counterparts …”

“…Moreover, to simulate experimental conditions aligning more closely with nanofluidic membrane systems, the interface properties governing the interaction between the PEL and electrolyte have been diversified. Parameters such as permittivity, diffusivity, and viscosity have been deliberately varied, effectively introducing an ion partitioning phenomenon at the interface between the PEL and the electrolyte. , Intriguingly, the role of the electric field type takes center stage in this study, with a distinction drawn between DC and AC electric fields, each characterized by distinctive wave functions. The inquiry encompasses an exploration of how these diverse electric field modes influence the complex interplay of ion transport within the nanochannels.…”

“…The rationale behind this divergence can be ascribed to the geometric disparity; specifically, the asymmetric nature of conical nanochannels leads to an amplified EDL overlap at the tip area, a phenomenon exceeding that observed in symmetric cylindrical counterparts. 33 Considering an alternative perspective, Figure 2e,f offer a radial portrayal of concentration differences at the tips of conical and cylindrical nanochannels. These plots explore scenarios where η ε = η D = η μ = 1 and η ε = η D = 0.8, η μ = 2, each shedding light on the influence of AC field types.…”

“…This observation holds true for both conical and cylindrical nanochannels, with the former exhibiting an ICP notably higher than that of the latter. The rationale behind this divergence can be ascribed to the geometric disparity; specifically, the asymmetric nature of conical nanochannels leads to an amplified EDL overlap at the tip area, a phenomenon exceeding that observed in symmetric cylindrical counterparts 33. Considering an alternative perspective, Figure2e,f offer a radial portrayal of concentration differences at the tips of conical and cylindrical nanochannels.…”

Layer-by-Layer Nanofluidic Membranes for Promoting Blue Energy Conversion

“…The characteristic length of these nanochannels/nanopores is comparable to the thickness of the electric double layer (EDL) formed on their walls, leading to unique electrokinetic phenomena, including ionic concentration polarization (ICP), ion selectivity, and ionic current rectification. − ICR occurs when a nanochannel/nanopore exhibits a diode-like or nonlinear current–voltage response to an applied voltage bias. In other words, ICR manifests as the generation of an ionic current in a specific direction under a voltage bias . Various factors contribute to the ICR within a nanochannel/nanopore, including geometric or charge distribution asymmetries, salt gradients, and environmental conditions.…”