Issue 6, 2014

Microfluidic flow-focusing in ac electric fields


We demonstrate the control of droplet sizes by an ac voltage applied across microelectrodes patterned around a flow-focusing junction. The electrodes do not come in contact with the fluids to avoid electrochemical effects. We found several regimes of droplet production in electric fields, controlled by the connection of the chip, the conductivity of the dispersed phase and the frequency of the applied field. A simple electrical modelling of the chip reveals that the effective voltage at the tip of the liquid to be dispersed controls the production mechanism. At low voltages (≲ 600 V), droplets are produced in dripping regime; the droplet size is a function of the ac electric field. The introduction of an effective capillary number that takes into account the Maxwell stress can explain the dependance of droplet size with the applied voltage. At higher voltages (≳ 600 V), jets are observed. The stability of droplet production is a function of the fluid conductivity and applied field frequency reported in a set of flow diagrams.

Graphical abstract: Microfluidic flow-focusing in ac electric fields

Article information

Article type
07 Oct 2013
02 Dec 2013
First published
09 Jan 2014
This article is Open Access
Creative Commons BY license

Lab Chip, 2014,14, 1099-1106

Microfluidic flow-focusing in ac electric fields

S. H. Tan, B. Semin and J. Baret, Lab Chip, 2014, 14, 1099 DOI: 10.1039/C3LC51143J

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