Flow Field Effect on Electric Double Layer during Streaming Potential Measurements

Abstract

It is typically assumed that flow field has very little or no effect on the electric double layer distribution. Here, we study this effect by means of a dilute electrolyte (deionized water) in a streaming potential mode for a 40-μm parallel-plate microchannel. By measuring the electrical potential downstream along the channel surface, we have shown that the potential distribution along a streamwise direction can be nonlinear. By means of a current continuity equation, we also presented numerical simulation results of potential distribution for pressure-driven flow with electrokinetic effects. The simulated results agree well with those from experiment. Results indicate that the conduction current in the streamwise direction is only a fraction of the streaming current. As a result, the ζ-potential values determined from streaming potential measurements are generally smaller than those from streaming current measurements. It is expected that this discrepancy would be smaller for a more concentrated electrolyte.

Effect of electrical double layer on electric conductivity and pressure drop in a pressure-driven microchannel flow

“…With the solutions of electric potential and charge density distribution in the channel, we can calculate the average electric conductivity of the solution in the channel, which is essential for the calculation of electric field buildup, or streaming potential, along the flow direction. The electric conductivity of an electrolyte is a summation of contributions from all ions, 15,13…”

“…13,14 The streaming current is proportional to the streaming potential and the fluid conductivity. In most previous research, 7,15 a constant value of electric conductivity independent of the EDL is used, although the value widely varies. Fundamentally, the electric conductivity of an electrolyte is a function of types of ions and ion concentrations.…”

Transient streaming potential in a finite length microchannel

“…Most analytical solutions, and sometimes numerical simulations, of electrokinetic transport processes are obtained employing the undisturbed ion concentration profiles based on the Poisson-Boltzmann equation. The obvious limitation of such an approach is its inability to predict any axial concentration variation [35] and, hence, any rejection of ions by the capillary. In contrast, the extended Nernst-Planck models applied to study ion transport through membrane pores predict a substantial axial variation of the ion concentrations in the capillary and, hence, a salt rejection.…”

Thermo-fluidic transport of electromagnetohydrodynamic flow of sodium alginate based Casson nano fluid passing through a porous microtube under the effect of streaming potential

“…An analytical solution of streaming potential and the periodical electro viscous effects in a pressure driven flow through a uniform microchannel is done by Gong et al [6]. An experimental investigation is provided by Lu et al [7] on the flow field effect on the EDL of the microchannel with the streaming potential. The previous studies are focused only on the electroosmotic flow.…”