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

Abstract

The effect of an electrical double layer (EDL) on microchannel flow has been studied widely, and a constant bulk electric conductivity is often used in calculations of flow rate or pressure drop. In our experimental study of pressure-driven micropipette flows, the pipette diameter is on the same order of magnitude as the Debye length. The overlapping EDL resulted in a much higher electric conductivity, lower streaming potential, and lower electroviscous effect. To elucidate the effect of overlapping EDL, this paper developed a simple model for water flow without salts or dissolved gases (such as CO(2)) inside a two-dimensional microchannel. The governing equations for the flow, the Poisson, and Nernst equations for the electric potential and ion concentrations and the charge continuity equation were solved. The effects of overlapping EDL on the electric conductivity, velocity distribution, and overall pressure drop in the microchannel were quantified. The results showed that the average electric conductivity of electrolyte inside the channel increased significantly as the EDL overlaps. With the modified mean electric conductivity, the pressure drop for the pressure-driven flow was smaller than that without the influence of the EDL on conductivity. The results of this study provide a physical explanation for the observed decrease in electroviscous effect for microchannels when the EDL layers from opposing walls overlap.

Electroviscous effect and convective heat transfer of pressure-driven flow through microtubes with surface charge-dependent slip

“…For the electrical conductivity of a symmetric electrolyte, it is the function of the ionic concentrations of the electrolyte and can be expressed as [26],…”

The effect of the electrical double layer on hydrodynamic lubrication: a non-monotonic trend with increasing zeta potential

“…Based on the previous studies, the bulk electrical conductivity of the lubricant under the influence of the EDL increases with the increasing absolute value of the zeta potential [26–27]. Hence, the EDL-dependent electrical conductivity of the lubricant must be considered during the analysis of the electroviscous effect and hydrodynamic lubrication.…”

“…Hence, the EDL-dependent electrical conductivity of the lubricant must be considered during the analysis of the electroviscous effect and hydrodynamic lubrication. The average bulk electrical conductivity under the influence of the EDL can be obtained as [26–27 31],…”

“…They found that the effect of the zeta potential on the load capacity resulted in a non-intuitive trend with increasing magnitude of zeta potential; however, further details and explanation were not given. In addition, the electroviscous effect is dependent on the electrical conductivity of the lubricant [26–27], which inevitably affects the hydrodynamic lubrication. However, most of the previous theoretical works neglected the variation of electrical conductivity of the lubricant considering the effect of the EDL.…”

Direct measurement of electric double layer in a nanochannel by electrical impedance spectroscopy

“…Many studies have measured electric currents in nanochannels for sensing and electrokinetic applications (Ren and Dongqing 2005;Ban et al 2010). However, most studies measured the end-to-end axial current of a nanochannel (i.e., the current flowing from one end to the other end of a nanochannel) (Wan 1997;Sze et al 2003;Schoch and Renaud 2005;Schoch et al 2008;Hughes et al 2008;Das and Chakraborty 2010;Perry et al 2010;Afanasiev et al 2011;Russell and Cohn 2012).…”