Bifurcation in the Steady-State Height of Colloidal Particles near an Electrode in Oscillatory Electric Fields: Evidence for a Tertiary Potential Minimum

Bifurcation in the Steady-State Height of Colloidal Particles near an Electrode in Oscillatory Electric Fields: Evidence for a Tertiary Potential Minimum

Application of an oscillatory electric field is known to alter the separation distance between micron-scale colloidal particles and an adjacent electrode. This behavior is believed to be partially due to a lift force caused by electrohydrodynamic flow generated around each particle, with previous wo...

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Bibliographic Details
Published in:Physical review. X Vol. 5; no. 1; p. 011023
Main Authors: Woehl, T. J., Chen, B. J., Heatley, K. L., Talken, N. H., Bukosky, S. C., Dutcher, C. S., Ristenpart, W. D.
Format: Journal Article
Language:English
Published: College Park American Physical Society 01-02-2015
Subjects:
Bifurcations
Binomial distribution
Colloids
Electric fields
Electrodes
Electrohydrodynamics
Fluid dynamics
Fluid flow
Fluorescence
LF electric fields
Microscopy
Particle interactions
Polystyrene resins
Potential energy
Separation
Steady state
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Summary:Application of an oscillatory electric field is known to alter the separation distance between micron-scale colloidal particles and an adjacent electrode. This behavior is believed to be partially due to a lift force caused by electrohydrodynamic flow generated around each particle, with previous work focused on identifying a single steady-state “height” of the individual particles over the electrode. Here, we report the existence of a pronounced bifurcation in the particle height in response to low-frequency electric fields. Optical and confocal microscopy observations reveal that application of a ∼100Hz field induces some of the particles to rapidly move several particle diameters up from the electrode, while the others move closer to the electrode. Statistics compiled from repeated trials demonstrate that the likelihood for a particle to move up follows a binomial distribution, indicating that the height bifurcation is random and does not result from membership in some distinct subpopulation of particles. The fraction of particles that move up increases with increased applied potential and decreased frequency, in a fashion qualitatively consistent with an energy landscape predicated on competition between electrohydrodynamic flow, colloidal interactions, and gravitational forces. Taken together, the results provide evidence for the existence of a deep tertiary minimum in the effective electrode-particle interaction potential at a surprisingly large distance from the electrode.
ISSN:2160-3308
2160-3308
DOI:10.1103/PhysRevX.5.011023