Extreme Levitation of Colloidal Particles in Response to Oscillatory Electric Fields

Journal Article · 03 May 2019 · Langmuir

DOI: https://doi.org/10.1021/acs.langmuir.9b00313 · OSTI ID:1560978

Bukosky, Scott C.  ^[1]; Hashemi Amrei, S. M. H. ^[2]; Rader, Sean P. ^[2]; Mora, Jeronimo ^[2]; Miller, Gregory H. ^[2]; Ristenpart, William D.  ^[2]

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1. Univ. of California, Davis, CA (United States). Dept. of Chemical Engineering; Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2. Univ. of California, Davis, CA (United States). Dept. of Chemical Engineering

Micron-scale colloidal particles suspended in electrolyte solutions have been shown to exhibit a distinct bifurcation in their average height above the electrode in response to oscillatory electric fields. Recent work by Hashemi Amrei et al. (Phys. Rev. Lett.,2018,121, 185504) revealed that a steady, long-range asymmetric rectified electric field (AREF) is formed when an oscillatory potential is applied to an electrolyte with unequal ionic mobilities. In this work, we use confocal microscopy to test the hypothesis that a force balance between gravity and an AREF-induced electrophoretic force is responsible for the particle height bifurcation observed in some electrolytes. We demonstrate that at sufficiently low frequencies, particles suspended in electrolytes with large ionic mobility mismatches exhibit extreme levitation away from the electrode surface (up to 50 particle diameters). This levitation height scales approximately as the inverse square root of the frequency for both NaOH and KOH solutions. Moreover, larger particles levitate smaller distances, while the magnitude of the applied field has little effect above a threshold voltage. A force balance between the AREF-induced electrophoresis and gravity reveals saddle node bifurcations in the levitation height with respect to the frequency, voltage, and particle size, yielding stable fixed points above the electrode that accord with the experimental observations. These results point toward a low-energy, non-fouling method for concentrating colloids at specific locations far from the electrodes.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC52-07NA27344
• OSTI ID: 1560978
• Report Number(s): LLNL-JRNL-758401; 946391
• Journal Information: Langmuir, Vol. 35, Issue 21; ISSN 0743-7463
• Publisher: American Chemical SocietyCopyright Statement
• Country of Publication: United States
• Language: English