Electro-hydrodynamic micro-fluidic mixerElectronic supplementary information (ESI) available: Video of effect of electric field on channel flow mixing. See http://www.rsc.org/suppdata/lc/b3/b306868b/

Abstract

Fluid mixing in microchannels is needed for many applications ranging from bio-arrays to micro-reactors, but is typically difficult to achieve. A simple geometry micro-mixer is proposed based on the electro-hydrodynamic (EHD) force present when the fluids to be mixed have different electrical properties and are subjected to an electric field. The electrodes are arranged so that the electric field is perpendicular to the interface between the two fluids, creating a transversal secondary flow. The technique is demonstrated experimentally using the flow of two liquids with identical viscosity and density, but different electrical properties. The volume flow rate and average velocity are 0.26 microl s(-1) and 4.2 mm s(-1), respectively, corresponding to a Reynolds number Re= 0.0174. The effect of a continuous (DC) electric field and two alternating (AC)- sinusoidal and square - electric fields is explored. At the appropriate parameter values, very good mixing takes place in less than 0.1 s, over a very short distance (within a fraction of the width 250 microm of the electrodes).

There can be turbulence in microfluidics at low Reynolds number

“…This is much higher than those used in other publications. 22,24 In addition, we also developed a velocimeter that can measure turbulence in microfluidics. The next challenge is how to measure and characterize turbulent flows in microfluidics using a spatiotemporal resolved velocimeter if there is turbulence in the microchannel.…”

Numerical analysis of mixing by electrothermal induced flow in microfluidic systems

“…This flow depends on electrical conductivity and permittivity of the buffer, the voltage and frequency of the applied electric field, and electrode configuration and dimensions of the microfluidic device. The dielectric force due to the variation of dielectric fluid properties, induced by nonthermal means, has also been reported in previous literature 19 as a means to facilitate mixing and is not in the scope of the present study.…”

Surface-enhanced Raman scattering microfluidic sensor

“…Electrical effects can be used for micromixing. El Moctar et al 54 describe a microfluidic mixer based on the electrohydrodynamic force present when the fluids to be mixed have different electrical properties and are subjected to an electrical field. Integrated electrodes are used to create an electric field perpendicular to the interface between the fluids in the microchannel, resulting in a transversal secondary flow that causes mixing.…”

“…More recently, Cecchini proposed an ultrafast and highthroughput droplet-based SERRS method that can make an efficient analysis at the submillisecond scale. 47 As shown in Active micromixers that use the disturbance generated by external field forces for the mixing process, such as electrical fields, 54,55 magnetic fields, 56 acoustic waves 57 and even electrostatic fields, 58 have been used to overcome the mixing problem in microfluidic channels. Active mixers show an excellent mixing performance and the flow control can be switched on or off, but it is relatively difficult to integrate it into a total microfluidic system because of the requirement of an external power source and controller.…”