Numerical investigation of the current transition regimes in nanochannels

Abstract

The concentration polarization phenomena and its effects represent one of the main challenges for the optimal operation of many nanofluidic systems. A numerical investigation of the different electric current transition regimes observed during the concentration polarization phenomena in nanochannels is performed. This included a 2D‐axisymmetric simulation of the nanofluidic system (reservoir‐nanochannel‐reservoir). From these simulations, a novel mechanism is discovered that explains that different current transition regimes. This driving mechanism involves the applied electric field penetration while the convective flow mechanism is found to be negligible. This differs with the classical statement that the mixing process with less depleted areas initiated by an electrokinetic vortex instability starts the overlimiting regime. Additionally, the numerical approach allows us to identify new characteristics of the linear‐limiting transition such as source‐like and saddle‐like points of the electric field streamlines. The three voltage–current regimes (linear, limiting and overlimiting) are explained by observing and quantifying changes in electric field, potential, ion concentration and ion concentration gradients within the system.

Overlimiting current near a nanochannel a new insight using molecular dynamics simulations

“…4 ) because the nanochannel is no longer ion selective as the EDL remains local to the nanochannel surface at 1M concentration 20 – 23 . Similarly, the recent study shows only the Ohmic behaviour when the surface charge density of the nanochannel becomes zero (as no EDL formation) 34 . Typically, the communication between the nanochannel wall atoms and ions are established through van der Waals (vdW) and electrostatic interactions.…”

“…The application of potential difference across the nanochannel creates an imbalance between cation and anion flux leading to the formation of the depletion and enrichment of the electrolyte solution across the interface of the nanochannel resulting in ion concentration polarization (ICP) 17 – 34 . The ion concentration polarization (ICP) effect leads to nonlinear I-V characteristics resulting in three regions, namely, Ohmic region, limiting resistance region (LRR) and overlimiting resistance region (OLR) (see Fig.…”

Ion Transport in Multi-Nanochannels Regulated by pH and Ion Concentration

“…Research indicates that independent diffusive transport within each nanochannel becomes feasible only when the distance of the nanochannel exceeds 56 times the diameter of the nanochannel. 67 With decreasing nanochannel distance, the flow field, electric field, and ion distribution within the multinanochannel system strongly depend on both the distance and the number of nanochannels. Figure S7 shows the results for the dual nanochannel system at pH = 8 and C KCl = 100 mM, where the distances between the nanochannels are 200 and 10 nm, respectively.…”

“…The lateral distance between adjacent nanochannels significantly influences their mutual interactions. Research indicates that independent diffusive transport within each nanochannel becomes feasible only when the distance of the nanochannel exceeds 56 times the diameter of the nanochannel . With decreasing nanochannel distance, the flow field, electric field, and ion distribution within the multinanochannel system strongly depend on both the distance and the number of nanochannels.…”

Ion Transport in pH-Regulated Double-Barreled Nanopores

“…This is because the phenomenon of ion concentration polarization (ICP) forms a depletion region as a large resistance; therefore, a higher electric potential is required to obtain the same current. 47 From the perspective of molecular dynamics, due to ion concentration polarization, an extended space charge zone forms between the double-barreled nanopore and reservoirs, and the extended space charge zone becomes a barrier for the entry of ions into the double-barreled nanopore. 48 At low C KCl and/or high pH, the ICP effect becomes significant.…”