Dynamic superconcentration at critical-point double-layer gates of conducting nanoporous granules due to asymmetric tangential fluxes

Abstract

A transient 10(6)-fold concentration of double-layer counterions by a high-intensity electric field is demonstrated at the exit pole of a millimeter-sized conducting nanoporous granule that permits ion permeation. The phenomenon is attributed to a unique counterion screening dynamics that transforms half of the surface field into a converging one toward the ejecting pole. The resulting surface conduction flux then funnels a large upstream electro-osmotic convective counterion flux into the injecting hemisphere toward the zero-dimensional gate of the ejecting hemisphere to produce the superconcentration. As the concentrated counterion is ejected into the electroneutral bulk electrolyte, it attracts co-ions and produce a corresponding concentration of the co-ions. This mechanism is also shown to trap and concentrate co-ion microcolloids of micron sizes too (macroions) and hence has potential application in bead-based molecular assays.

Graphene-Based Planar Nanofluidic Rectifiers

“…Fundamental to these applications is the ability of the nanochannel or nanopore to regulate ion transport, thus facilitating ion enrichment and depletion and current rectification as a consequence of the ion permselectivity under confinement. Ion enrichment and depletion typically arise at the interface between the nanofluidic channels and the microfluidic reservoirs supplying the channels ,, as a result of the formation of a diffusion layer enriched with co-ions at the micro-/nano-interface on the entrance side to the nanochannels (the side where the counterions enter) compared with a corresponding counterion depletion region at the exit (the side where counterions leave) ,, similar to that in nanoporous permselective membranes or granules, − leading to saturation in the ionic current beyond a critical voltage . Ion current rectificationthe ability to conduct ion current preferentially in one direction and inhibit the current flow in the opposite direction when switching the bias voltage, in analogy to a diodeon the other handis a consequence of asymmetry that exists along the nanochannel, be it in the buffer, surface charge, or geometry …”

Microfluidic Systems with Ion-Selective Membranes

“…Ion enrichment at one pole of an ion-exchange granule and vortex pair generation at the other pole when an electric field is applied across an ion-selective granule(74). (a) Convective charging of the granule by asymmetric vortices at the right.…”

Electrokinetic and Electroconvective Effects in Ternary Electrolyte Near Ion-Selective Microsphere

“…The first concept is based on using a complex planar system of channels, ion-exchange membranes and electrodes [ 5 , 19 ]. The second concept of the device design is based on using a spherical geometry [ 20 , 21 ]. The first approach is characterized by a high degree of analyte concentration, and the second one is distinguished by simplicity and versatility, because in such geometry one device can simultaneously perform the roles of a micro-pump [ 22 ], a micromixer [ 20 , 23 ], a microreactor, and a microseparator [ 21 ].…”