Influence of finite ion size and dielectric decrement on the ion current rectification in a single conical nanopore

Abstract

The ion current rectification (ICR) arising due to the transport of ionized liquids within a geometrically asymmetric nanopore is of great significance for the development of smart nanogadgets with unique working capabilities. Though the theoretical framework for the ICR is well developed, the influence of the finite size of ions on the ICR phenomena had not been addressed before. The ion steric repulsion due to finite ion size and dielectric decrement of the medium creates a counterion saturation. In this study, a modified electrokinetic model is adopted to describe the ICR phenomena of a single conical nanopore by considering the hydrated ions as finite-sized dielectric charged spheres. The Nernst–Planck equations for ion transport are modified to incorporate the short-range ion steric interactions modeled by the Boublik–Mansoori–Carnahan–Starling–Leland equation as well as Born force and dielectrophoretic force acting on the hydrated ions engender by the ion–solvent interactions. The counterion saturation attenuates the shielding effect of the surface charge of the nanopore leading to a larger ζ-potential and hence, a larger volume flux and reduced conduction. We find that the ion steric interactions and the dielectric decrement significantly influence the ICR phenomena as well as the ion selectivity of a conical nanopore, especially for moderate to high range of surface charge density, bulk concentration, and applied bias. We find that ICR varies linearly with temperature; however, the variation is found to be marginal. Our results show that the volume flux and the rectification factor of the conical nanopore can be suitably tuned by adding salt of larger counterion size or multivalent ions.

Chemiosomotic flow in a soft conical nanopore: harvesting enhanced blue energy

“…Thus, for the sake of simplicity and primarily to capture the underlying physics behind pH gradient, we have neglected any nonlinear effects such as finite ion size, a dielectric decrease, and temperature-dependent parameters. [31][32][33] The conservation of ionic species follows the Nernst-Planck equation, which, in a steady-state can be expressed as…”

“…Thus, for the sake of simplicity and primarily to capture the underlying physics behind pH gradient, we have neglected any nonlinear effects such as finite ion size, a dielectric decrease, and temperature-dependent parameters. 31–33 The conservation of ionic species follows the Nernst-Planck equation, which, in a steady-state can be expressed asHere, c i , N i , z i , D i respectively, represent the concentration, flux, valence, and diffusivities of i th, i = 1, 2, 3, and 4 ionic species, respectively, and R , F , and T are the universal gas constant, Faraday constant, and absolute temperature, respectively. The electric potential ϕ is governed by the local space charge density of the electrolyte solution and it follows the Poisson equation:where, j is a binary variable, value of which is either 1 or 0 depending upon the region within the PEL or outside the PEL, respectively.…”

Polydopamine-Induced Modification on the Highly Charged Surface of Asymmetric Nanofluidics: A Strategy for Adjustable Ion Current Rectification Properties

“…Biological ion channels are a critical component of cell or subcellular membranes in the regulation of ion transport for diverse biological processes. , The biological ion channels are naturally asymmetric in structure and surface charge distribution, which is highly associated with the selectivity of ion transport. − Ion current rectification (ICR) is a fundamental ion-transport phenomenon in asymmetric ion channels that presents ion enrichment or depletion under an opposite bias voltage. − The ICR phenomenon was first discovered in quartz nanopipettes and then received widespread research coverage in biological ion channels, organic or inorganic nanopore/nanochannel, − heterogeneous membrane − and solid-state electrolytes . Significant progress in understanding the ICR effect brought a wide application of asymmetric nanopore/nanochannel in ionic circuits, − ion permeability-selectivity, − DNA sequencing, − biosensors, − and water-energy nexus. − …”

Numerical Investigation of Diffusioosmotic Flow in a Tapered Nanochannel

“…Inversion of ICR has also been reported due to concentration depletion at the tip [ 53 ] and at the over-limiting current threshold [ 54 ]. Research on the numerical front focused on the influence of various control parameters on ICR, for instance, the effect of nanopore tip dimension [ 55 ], non-uniform surface charge density [ 56 , 57 , 58 ], pore length [ 59 ], solution pH [ 60 , 61 , 62 ], and ionic size [ 63 ]. Concerning the tapered nanofluidics, on the one hand, numerical simulations performed by neglecting the flow field have reported surface charge density, salt concentration gradient, and nanopore geometry as the primary factors affecting ICR in tapered nanopores [ 48 , 54 ].…”