Next Article in Journal
Experimental Setup for Dynamic Analysis of Micro- and Nano-Mechanical Systems in Vacuum, Gas, and Liquid
Next Article in Special Issue
A Continuous Flow-through Microfluidic Device for Electrical Lysis of Cells
Previous Article in Journal
High Precision Thermoforming 3D-Conformable Electronics with a Phase-Changing Adhesion Interlayer
Previous Article in Special Issue
Modeling the AC Electrokinetic Behavior of Semiconducting Spheres
Article Menu
Issue 3 (March) cover image

Export Article

Open AccessArticle

Characterization of Chaotic Electroconvection near Flat Inert Electrodes under Oscillatory Voltages

1
School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ 85287, USA
2
Center for Turbulence Research, Stanford University, Stanford, CA 94305, USA
*
Author to whom correspondence should be addressed.
Micromachines 2019, 10(3), 161; https://doi.org/10.3390/mi10030161
Received: 1 February 2019 / Revised: 20 February 2019 / Accepted: 20 February 2019 / Published: 26 February 2019
(This article belongs to the Special Issue AC Electrokinetics in Microfluidic Devices)
  |  
PDF [4705 KB, uploaded 26 February 2019]
  |  

Abstract

The onset of electroconvective instability in an aqueous binary electrolyte under external oscillatory electric fields at a single constant frequency is investigated in a 2D parallel flat electrode setup. Direct numerical simulations (DNS) of the Poisson–Nernst–Planck equations coupled with the Navier–Stokes equations at a low Reynolds number are carried out. Previous studies show that direct current (DC) electric field can create electroconvection near ion-selecting membranes in microfluidic devices. In this study, we show that electroconvection can be generated near flat inert electrodes when the applied electric field is oscillatory in time. A range of applied voltage, the oscillation frequency and the ratio of ionic diffusivities is examined to characterize the regime in which electroconvection takes place. Similar to electroconvection under DC voltages, AC electroconvection occurs at sufficiently high applied voltages in units of thermal volts and is characterized by transverse instabilities, physically manifested by an array of counter-rotating vortices near the electrode surfaces. The oscillating external electric field periodically generate and destroy such unsteady vortical structures. As the oscillation frequency is reduced to O ( 10 1 ) of the intrinsic resistor–capacitor (RC) frequency of electrolyte, electroconvective instability is considerably amplified. This is accompanied by severe depletion of ionic species outside the thin electric double layer and by vigorous convective transport involving a wide range of scales including those comparable to the distance L between the parallel electrodes. The underlying mechanisms are distinctly nonlinear and multi-dimensional. However, at higher frequencies of order of the RC frequency, the electrolyte response becomes linear, and the present DNS prediction closely resembles those explained by 1D asymptotic studies. Electroconvective instability supports increased electric current across the system. Increasing anion diffusivity results in stronger amplification of electroconvection over all oscillation frequencies examined in this study. Such asymmetry in ionic diffusivity, however, does not yield consistent changes in statistics and energy spectrum at all wall-normal locations and frequencies, implying more complex dynamics and different scaling for electrolytes with unequal diffusivities. Electric current is substantially amplified beyond the ohmic current at high oscillation frequencies. Also, it is found that anion diffusivity higher than cation has stronger impact on smaller-scale motions ( 0.1 L). View Full-Text
Keywords: Electroconvection; AC electrokinetics; inert electrodes Electroconvection; AC electrokinetics; inert electrodes
Figures

Figure 1

This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

Supplementary material

SciFeed

Share & Cite This Article

MDPI and ACS Style

Kim, J.; Davidson, S.; Mani, A. Characterization of Chaotic Electroconvection near Flat Inert Electrodes under Oscillatory Voltages. Micromachines 2019, 10, 161.

Show more citation formats Show less citations formats

Note that from the first issue of 2016, MDPI journals use article numbers instead of page numbers. See further details here.

Related Articles

Article Metrics

Article Access Statistics

1

Comments

[Return to top]
Micromachines EISSN 2072-666X Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
Back to Top