Chaotic electroosmotic mixing

Various active micromixers using 2-D time-dependent flow to achieve chaotic advection have been developed [16-19]. Since electroosmosis is very attractive for manipulating fluids in LOC devices, a chaotic electroosmotic stirrer developed by Qian and Bau [20] is described as an example to achieve chaotic advection and mixing by 2-D time-dependent electroosmotic flow. 

Qian S, Bau H (2002) A chaotic electroosmotic stirrer. Anal Chem 74(15) 3616-3625 Glasgow I, Batton J, Aubry N (2004) Electroosmotic mixing in microchannels. Lab Chip 4(6) 558-562... 

Figure 1. Schematics of the continuous chaotic stirrer developed by Kim and Beskok [25], The stirrer consists of periodically repeating mixing bocks with zeta potential patterned surfaces (a) and an electric field parallel to the x-axis is externally applied resulting in an electroosmotic flow (b). Combining a unidirectional (x-direction) pressure-driven flow (c) with electroosmotic flow under time-periodic external electric field (in the form of a Cosine wave with a frequency ra), a 2-D time-periodic flow is induced to achieve chaotic stirring in the mixer. Two fluid streams colored with red and blue are pumped into the mixer from the left and are almost well mixed after eight repeating mixing blocks for Re = 0.01, St = I2%, Pe= 1,000, and T = 0.8(d).

H.J. Kim and A. Beskok, Numerical Modeling of Chaotic Mixing in Electroosmotically Stirred Continuous Flow Mixers, ASME J. Heat Transfer 131(9) 092403 (2009). 

Applications of time-wise periodic alterations of the zeta potential along the microchaimel walls to induce an electroosmotic chaotic advection effect can improve mixing. It was shown that both a spatial and a temporal control of the zeta potential could be achieved by applying a field effect (i.e., a capacitive effect). The effect of periodically switching between several different... 

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