Tetraalkylammonium Cations Conduction through a Single Nanofluidic Diode: Experimental and Theoretical Studies

Abstract

We describe experimentally and theoretically the concentration-dependent conduction of tetraalkylammonium (TAA +) cations through a nanofluidic diode fabricated in a polymer membrane via asymmetric track-etching techniques. This single-pore membrane exhibits current rectification characteristics because of the ionized carboxylate groups on the pore surface. We use aqueous solutions of potassium (K +), ammonium (A +), tetramethylammonium (TMA +), tetraethylammonium (TEA +), and tetrabutylammonium (TBA +) ions with concentrations ranging from 50 to 500 mM under acidic (pH 3.5) and physiological (pH 6.5) conditions. Compared with the K + and A + ions, the TMA + , TEA + , and TBA + ions show relatively low rectified ion currents because the cation hydrophobicity increases with the alkyl chain. At low concentrations and acidic conditions, an inversion in the current rectification characteristics is observed, which is attributed to the adsorption of the organic cations on the pore surfaces. The experimental results can be analyzed in terms of the Poisson-Nernst-Planck equations and the geometrical and electrical single pore characteristics for the different ions, pH values, and salt concentrations employed. This theoretical approach is qualitative and could be extended further to include a selfconsistent theoretical treatment of the ionic adsorption and surface charge equilibria.

Electric Migration of Hydrogen Ion in Pore-Voltammetry Suppressed by Nafion Film

“…A macroscopic concept of the rectification is composed of (i) geometric obstacle of the ion transport through the hole in the closed state and (ii) the localized accumulation of electrolyte owing to ion-exchange membrane in the open state [19,29,30]. A concept from the microscopic viewpoints is a gate linked to the potential distribution in the double-layer or on pore walls [31][32][33][34][35][36][37] as well as molecular instability in a hydrodynamic vortex [38,39].…”

Microhole‐voltammograms Controlled by Solution Reservoir at Cationic and Anionic Ion Exchange Membranes

“…In contrast, microscopic asymmetry involves chemical modification on walls of holes [5, 6], selection of materials of holes [7–10] and usage of a nanopipette coated with surfactants [15–18]. It includes a gate switched by the potential distribution in double‐layers or on hole walls [33–38] as well as molecular instability in hydrodynamic vortex [39, 40].…”

Impact of Polyelectrolyte Multilayers on the Ionic Current Rectification of Conical Nanopores

“…For the last two decades, single nanopore technology has contributed to the emergence and design of nanofluidic responsive systems. − It has provided a deep understanding of the transport from the simple electrolyte to the (bio)­macromolecule (DNA, polymer or protein) at the nanoscale and contributed to the development of new analytical devices. , Nanopores with a dissymmetry of charge or shape are also particularly fascinating for their ionic diode behavior. − They are usually obtained using a polymer film [poly­(ethylene terephthalate) (PET), PC, or PI] by a track-etched technique under a dissymmetrical condition to ensure a conical shape . In such a nanopore, the ionic current rectification (ICR) comes from a depletion of anions or cations inside the nanopore. , It can be tuned by the functionalization of the nanopore inner surface walls.…”