Concentration polarization, surface currents, and bulk advection in a microchannel

Nielsen, Christoffer Peder; Bruus, Henrik

doi:10.1103/physreve.90.043020

Cited by 51 publications

(80 citation statements)

References 42 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…With the microscopic imaging of electrokinetic flow and electrical measurements, we can separate the effects of the EOF and SC depending on the geometrical confinement. Consistent with the theory [31,32], surface conduction dominates in shallow micro (or nano) channels and electroosmotic surface convection dominates in microchannels with a minimum OLC at the predicted transition around 8 μm depth, but the theory fails to predict complex EOF vortices and unstable convection, as the channel depth is increased further. Millimeter scale fluidic experiments, which are quite far from the geometrical range of the present work, should be required for detailed characterization of the electro-osmotic instability as suggested by Ref.…”

Section: Fig 2 (Color Onlinementioning

confidence: 53%

“…The SC mechanism has also been confirmed in straight nanopores with controlled surface charge by again predicting the current-voltage relation and by ex situ imaging of metal electrodeposits grown along the pore walls by SC [36]. However, no theory or experiment has shed light on the roles of SC and EOF during transient deionization shock propagation, and several assumptions of the steady-state scaling theory have been called into question by direct numerical simulations [32].…”

mentioning

confidence: 97%

“…The increasing d 4=5 scaling for EOF is also consistent with the data for the thicker microchannels as a possible limiting scaling law, although the data are not conclusive. Since direct numerical simulations have recently called some assumptions of the scaling theory into question [32], our data can guide further theoretical developments. Remarkably, however, the minimum conductance around d ¼ 8 μm is identical to the theoretical prediction of the critical depth from the intersection of the two scaling laws [31].…”

mentioning

confidence: 99%

“…A unified scaling theory of OLC through an electrolyte confined within a charged microchannel has recently been developed [31,32], but direct experimental confirmation is still lacking. The theory predicts a transition between two new mechanisms, surface conduction (SC) and electroosmotic flow (EOF), that dominate in nanochannels and microchannels, respectively.…”

mentioning

confidence: 99%

See 3 more Smart Citations

Experimental Verification of Overlimiting Current by Surface Conduction and Electro-Osmotic Flow in Microchannels

et al. 2015

View full text Add to dashboard Cite

Direct evidence is provided for the transition from surface conduction (SC) to electro-osmotic flow (EOF) above a critical channel depth (d) of a nanofluidic device. The dependence of the overlimiting conductance (OLC) on d is consistent with theoretical predictions, scaling as d −1 for SC and d 4=5 for EOF with a minimum around d ¼ 8 μm. The propagation of transient deionization shocks is also visualized, revealing complex patterns of EOF vortices and unstable convection with increasing d. This unified picture of surface-driven OLC can guide further advances in electrokinetic theory, as well as engineering applications of ion concentration polarization in microfluidics and porous media.

show abstract

Section: Fig 2 (Color Onlinementioning

confidence: 53%

mentioning

confidence: 97%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 2 more Smart Citations

Experimental Verification of Overlimiting Current by Surface Conduction and Electro-Osmotic Flow in Microchannels

et al. 2015

View full text Add to dashboard Cite

show abstract

“…Sketch of a charged cylindrical pore subjected to water flow, electrical current, and salt flux between a high-salinity (left) and low-salinity (right) reservoir. and diffusion dominate, although nonequilibrium structures, such as "salt fingers" extending along the pore surfaces, can arise in microchannels, if electro-osmotic convection dominates [41,44,45,48]. Here, we neglect such effects and focus on deriving the consequences of local (but not global) quasiequilibrium.…”

Section: Introductionmentioning

confidence: 99%

Analysis of electrolyte transport through charged nanopores

et al. 2016

View full text Add to dashboard Cite

We revisit the classical problem of flow of electrolyte solutions through charged capillary nanopores or nanotubes as described by the capillary pore model (also called "space charge" theory). This theory assumes very long and thin pores and uses a one-dimensional flux-force formalism which relates fluxes (electrical current, salt flux, and fluid velocity) and driving forces (difference in electric potential, salt concentration, and pressure). We analyze the general case with overlapping electric double layers in the pore and a nonzero axial salt concentration gradient. The 3×3 matrix relating these quantities exhibits Onsager symmetry and we report a significant new simplification for the diagonal element relating axial salt flux to the gradient in chemical potential. We prove that Onsager symmetry is preserved under changes of variables, which we illustrate by transformation to a different flux-force matrix given by Gross and Osterle [J. Chem. Phys. 49, 228 (1968)]. The capillary pore model is well suited to describe the nonlinear response of charged membranes or nanofluidic devices for electrokinetic energy conversion and water desalination, as long as the transverse ion profiles remain in local quasiequilibrium. As an example, we evaluate electrical power production from a salt concentration difference by reverse electrodialysis, using an efficiency versus power diagram. We show that since the capillary pore model allows for axial gradients in salt concentration, partial loops in current, salt flux, or fluid flow can develop in the pore. Predictions for macroscopic transport properties using a reduced model, where the potential and concentration are assumed to be invariant with radial coordinate ("uniform potential" or "fine capillary pore" model), are close to results of the full model.

show abstract

Deionization shocks in crossflow

et al. 2021

View full text Add to dashboard Cite

Shock electrodialysis is a recently developed electrochemical water treatment method that shows promise for water deionization and ionic separations. Although simple models and scaling laws have been proposed, a predictive theory has not yet emerged to fit experimental data and enable system design. Here, we extend and analyze existing “leaky membrane” models for the canonical case of a steady shock in crossflow, as in recent experimental prototypes. Two‐dimensional numerical solutions are compared with analytical boundary‐layer approximations and experimental data. The boundary‐layer theory accurately reproduces the simulation results for desalination, and both models predict the data collapse of the desalination factor with dimensionless current, scaled to the incoming convective flux of cations. The numerical simulation also predicts the water recovery increase with current. Nevertheless, neither approach can quantitatively fit the transition from normal to over‐limiting current, which suggests gaps in our understanding of extreme electrokinetic phenomena in porous media.

show abstract

Concentration polarization, surface currents, and bulk advection in a microchannel

Cited by 51 publications

References 42 publications

Experimental Verification of Overlimiting Current by Surface Conduction and Electro-Osmotic Flow in Microchannels

Experimental Verification of Overlimiting Current by Surface Conduction and Electro-Osmotic Flow in Microchannels

Analysis of electrolyte transport through charged nanopores

Deionization shocks in crossflow

Contact Info

Product

Resources

About