Electrohydrodynamics around single ion-permselective glass beads fixed in a microfluidic device

Abstract

This work demonstrates by direct visualization using confocal laser scanning microscopy that the application of electrical fields to a single-fixed, ionpermselective glass bead produces a remarkable complexity in both the coupled mass and charge transport through the bead and the coupled electrokinetics and hydrodynamics in the adjoining bulk electrolyte. The visualization approach enables the acquisition of a wealth of information, forming the basis for a detailed analysis of the underlying effects (e.g., ion-permselectivity, concentration polarization, nonequilibrium electroosmotic slip) and an understanding of electrohydrodynamic phenomena at charge-selective interfaces under more general conditions. The device used for fixing single beads in a microfluidic channel is flexible and allows to investigate the electrohydrodynamics in both transient and stationary regimes under the influence of bead shape, pore size and surface charge density, mobile phase composition, and applied volume forces. This insight is relevant for the design of microfluidic/nanofluidic interconnections and addresses the ionic conductance of discrete nanochannels, as well as nanoporous separation and preconcentration units contained as hybrid configurations, membranes, packed beds, or monoliths in lab-on-a-chip devices.

Electrochromatographic retention of peptides on strong cation‐exchange stationary phases

“…4 in [46]; see also Figs. 4 and 7 in [47]). An increase of applied field strength (which increases the electrical current through the particle) and a decrease of electrolyte ionic strength (which increases the particle's ion-permselectivity) leads to steeper concentration gradients in the CP zones, at least within certain limits [45].…”

“…Transport of charged species in the CP zones is diffusion limited. In multiparticle systems like packed beds, CP zones develop around each spatially discrete particle [43][44][45][46][47]65]. CP has been intensively investigated in membrane science over the past decades.…”

“…Compared with the unpacked capillaries used in CZE, coupled mass and charge transport in packed capillaries are much more complex due to concentration polarization (CP), which is induced locally around any stationary phase particle of the bed by the applied electrical field [43][44][45][46][47]. CP originates in electrical double layer (EDL) overlap inside the charged pores of porous particles that are characterized by mesopore (and even micropore) sizes.…”

“…It involves the formation of background ion concentration gradients at charge-selective interfaces upon the passage of an electrical current normal to these interfaces [50]. CP for a cation-selective stationary phase particle is characterized by a depleted CP zone along its anodic hemisphere, where counterions enter the particle in the direction of the applied field, and an enriched CP zone along its cathodic hemisphere, where counterions leave the particle [43][44][45][46][47].…”

Ion bridges in microfluidic systems

“…They bypassed the electric field to solve this problem. About the concentration polarization around the nanostructure, there have been a number of reports (Datta et al 2006;Ehlert et al 2008;Holtzel and Tallarek 2007;Jin et al 2007;Nischang et al 2008;Rubinstein et al 2005;Tallarek et al 2005;Zaltzman and Rubinstein 2007). Holtzel and Tallarek reviewed the literature on the concentration polarization and ionic conductivity of nanostructure with permselectivity (Fig.…”