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Abstract: In non-dilute colloidal suspensions, gradients in particle volume fractionresult in gradients in electrical conductivity and permittivity. An externallyapplied electric field couples with gradients in electrical conductivity andpermittivity and, under some conditions, can result in electric body forcesthat drive the flow unstable forming vortices. The experiments are conducted insquare 200 micron PDMS microfluidic channels. Colloidal suspensions consistedof 0.01 volume fraction of 2 or 3 micron diameter polystyrene particles in 0.1mM Phosphate buffer and 409 mM sucrose to match particle-solution density. ACelectric fields at 20 Hz and strength of 430 to 600 V-cm were used. We presenta fluid dynamics video that shows the evolution of the particle aggregation andformation of vortical flow. Upon application of the field particles aggregateforming particle chains and three dimensional structures. These particles formrotating bands where the axis of rotation varies with time and can collide withother rotating bands forming increasingly larger bands. Some groups becomevortices with a stable axis of rotation. Other phenomena showed include counterrotating vortices, colliding vortices, and non-rotating particle bands withinternal waves.

Autor: Carlos L. Perez, Jonathan D. Posner


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