Hello,
in dielectrophoresis experiments I can observe vortices at the electrodes and wonder where they come from. I am particularly surprised why the vortex size at both electrodes is not the same. I use ultrapure water, with 0.05 v% surfactant (Tween 20), KOH to adjust the pH to 7 and KCl to increase the conductivity to 1.5 µS/cm as fluid. A voltage of 3 kV at 15 kHz is applied via two platinum electrodes and we perform trapping of micrparticles by pDEP in arrays of cylindrical posts in microchannels. The experimental design is discussed in the publication Pesch et al., Scientific Reports 8(1), 10480, 2018 (doi: 10.1038/s41598-018-28735-w). There is also a picture attached showing the experimental design with placement of electrodes. Vortices are now created at the electrodes, which are visible both by tracing particle trajectories or by introducing a dye pulse into the system and tracking how the dye behaves. A change in the fluorescence of Rhodamine B to indicate a temperature change due to Joule heating could not be detected, i.e., we assume the vortices are not caused by temperature differences. Connecting a capacitor after the amplifier to eliminate an DC offset does not create any improvement. Has anyone observed something like this before or knows the reason for the vortices and also a way to weaken them?
A video is attached showing the vortice after application of the electric field. The electrode is at the top border of the video, just out of sight.
Thank you.
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The vortices could possibly be from AC electroosmosis. Your conductivity and the applied frequency seem about the right range for inducing AC electroosmosis. Do you see any frequency dependence for the vortices? If AC electroosmosis is causing the vortices, they should reduce by increasing the frequency if that works for your specific case as you are trying to induce pDEP.
Thank you very much for your comments and suggestions Dhinakaran Veeman and Paresa Modarres . Due to limitations of our amplifier we could only check the frequency dependence up to 20 kHz at constant high voltage. In the range of 10 to 20 kHz we could rather observe an increase of the vortex size with frequency. Is anyone aware of a way to simulate ACEO effects in such iDEP channels? It would be great to be able to simulate the vortex effects around the electrodes, to see if a frequency increase would help and to be able to select a suitable amplifier.
Dear Researcher Laura Weirauch , the electrode dimension plays a major role in forming the voices. Kindly look into the article Article Applications of dielectrophoretic/electro-hydrodynamic “zipp...
Hey. Just as an annotation. According to the user's guide of the microfluidics module of comsol, one can simulate ACEO using the same approach as for DC electroosmosis as long as the "frequency is sufficiently low".
Is anyone aware of a publication which shows the temperature distribution around the electrodes in iDEP devices? The resulting temperature gradient could give rise to electrothermal movement.
Two reasons might cause the vortices at electrodes in dielectrophoresis experiments. First, the Joule heating effect because you are using high voltage and high fluid conductivity. The current flowing in the medium causes non-uniform heating (temperature gradient), which is responsible for the fluid circulation and drag velocity. The second reason is the electric double layer (EDL) created on the electrode surface causing electroosmotic flow. The best way to avoid the EDL is by using frequencies higher than quotient fluid conductivity over fluid permittivity (σ/ε) . I suggest you to use low fluid conductivity and high frequencies.
Check the following article
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