2007/11/29 by Brian D. Storey, Storey, Brian D., Lee R. Edwards +5
Chemistry · Engineering · Physics and Astronomy · #Electrohydrodynamics and Fluid Dynamics #Electrostatics and Colloid Interactions #FOS: Physical sciences #Microfluidic and Bio-sensing Technologies #Other Condensed Matter (cond-mat.other) #cond-mat.other
paper · pdf · doi:10.48550/arxiv.0711.4812
12 pages
arxiv created 2007/11/29 · openalex publication_date 2007/11/29 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The current theory of alternating-current electro-osmosis (ACEO) is unable to explain the experimentally observed flow reversal of planar ACEO pumps at high frequency (above the peak, typically 10-100 kHz), low salt concentration (1-1000 μM), and moderate voltage (2-6 V), even if taking into account Faradaic surface reactions, nonlinear double-layer capacitance and bulk electrothermal flows. We attribute this failure to the breakdown of the classical Poisson-Boltzmann model of the diffuse double layer, which assumes a dilute solution of point-like ions. In spite of low bulk salt concentration, the large voltage induced across the double layer leads to crowding of the ions and a related decrease in surface capacitance. Using several mean-field models for finite-sized ions, we show that steric effects generally lead to high frequency flow reversal of ACEO pumps, similar to experiments. For quantitative agreement, however, an unrealistically large effective ion size (several nm) must be used, which we attribute to neglected correlation effects.