Related Experiment Video
Updated: Aug 19, 2026

AC Electrokinetic Phenomena Generated by Microelectrode Structures
Published on: July 28, 2008
Evidence of multiple electrohydrodynamic forces acting on a colloidal particle near an electrode due to an
Jeffrey A Fagan1, Paul J Sides, Dennis C Prieve
1Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
Abstract:
Total internal reflection microscopy was used to monitor the elevation of 4-7.5 mum diameter particles near an electrode in response to an oscillating electric field with amplitude up to 8.5 kV/m. The media were 0.15 mM electrolyte solutions of HNO(3), NaHCO(3), and KOH, and the frequency band was 40 Hz to 10 kHz. Polystyrene-sulfonate particles were used in bicarbonate and KOH solutions, while polystyrene-amine particles were used in nitric acid. At frequencies less than 500 Hz, large oscillations in elevation at the driving frequency with small superimposed Brownian excursions were observed. At frequencies above 1 kHz, deterministic oscillations in elevation were negligible compared to Brownian fluctuations, which allowed transformation of histograms of elevations into potential energy profiles. The ac field drew the particle closer on average to the electrode in KOH solutions (compared to the no-field average elevation) and the field pushed the particle farther from the electrode in NaHCO(3). In HNO(3) a reversal of average height was observed at a frequency of 300 Hz at 1.7 kV/m with the particle being drawn closer to the electrode at low frequencies and being pushed away at higher frequencies. The reversal reflects two different electrohydrodynamic mechanisms. Analysis of the data at a high frequency (10 kHz) revealed a net force that was attractive in KOH and repulsive in HNO(3). This net force scaled with E(2)omega(-)(1), where E is the amplitude and omega is the frequency.
Related Concept Videos
The Electrical Double Layer
Processes at Electrodes
Electrochemical Systems
Electrodeposition
Electrodeposition can...
The Colloidal State
Colloidal precipitates

