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

Abstract

In this paper, we report for the first time overlimiting current near a nanochannel using all-atom molecular dynamics (MD) simulations. Here, the simulated system consists of a silicon nitride nanochannel integrated with two reservoirs. The reservoirs are filled with $${0.1} \, \hbox {M}$$ 0.1 M potassium chloride (KCl) solution. A total of $${\sim } 1.1$$ ∼ 1.1 million atoms are simulated with a total simulation time of $${\sim } 1 {\mu s}$$ ∼ 1 μ s over $${\sim }$$ ∼ 30000 CPU hours using 128 core processors (Intel(R) E5-2670 2.6 GHz Processor). The origin of overlimiting current is found to be due to an increase in chloride ($${Cl^-}$$ C l - ) ion concentration inside the nanochannel leading to an increase in ionic conductivity. Such effects are seen due to charge redistribution and focusing of the electric field near the interface of the nanochannel and source reservoir. Also, from the MD simulations, we observe that the earlier theoretical and experimental postulations of strong convective vortices resulting in overlimiting current are not the true origin for overlimiting current. Our study may open up new theories for the mechanism of overlimiting current near the nanochannel interconnect devices.

All-Atom Molecular Dynamics Simulations of Communication Between Nanochannel Arrays

“…The LJ parameters for all atom types are taken the same similar to our earlier work. 45 For the calculations of LJ interactions, a cutoff distance of 1.2 nm with switching functions starting at 1 nm was considered. Also, for electrostatic calculations, the particle mesh Ewald (PME) method is employed with a grid spacing of 0.12 nm.…”

“…The overall simulation system includes ∼2 to 4 million atoms and is simulated for a total simulation time of ∼0.7 μs over ∼9000 CPU hours (Intel Xeon Gold 6142 16core, 2.6 GHz processor) with a GPU acceleration (Nvidia V100 GPUs). The steady state of the system is monitored by measuring the ionic current inside a nanochannel using the following relation 5,45,50,51 (see Figure S1).…”

“…56−58 Moreover, the ions that overscreen the nanochannel surface charge density are driven away at higher voltages (>30 V) leading to the predominant transport of K + ions inside the channel. 45,58 To demonstrate the effect of charge inversion, the surface charge density is reduced from −0.6 to −0.1 C/m 2 (Figure S11). The results revealed the same pattern of communication though the charge inversion is not observed (at σ = −0.1 C/m 2 ).…”

Ion Transport in pH-Regulated Double-Barreled Nanopores

“…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. 32 Thus, the nonlinear I−V relationship can be observed at pH = 9 and C KCl = 1 mM due to a more serious ICP phenomenon, which will be further discussed in the next section.…”

“…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 . 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 . At low C KCl and/or high pH, the ICP effect becomes significant .…”