3.2.1. ACEO micromixer
The MVs produced around polarizable electrodes have been employed for the ACEO-based mixing of different solutions in microchannels. The first theoretical ACEO mixers were developed by Squires and Bazant (Bazant & Squires, 2004; Todd M Squires & Bazant, 2004) and Sasaki et al. (Sasaki, Kitamori, & Kim, 2006), where they introduced a pair of meandering electrodes for rapid mixing of liquids inside microchannels. The results demonstrated 90% mixing efficiency, where one-millimeter length of mixing using the active ACEO was equivalent to 25 mm length of passive mixing using the diffusional mechanism. The effective mixing in this system lasts 0.18 s which was 20 folds faster than diffusional mixing. Kim et al. (B. J. Kim, Yoon, Sung, & Smith, 2007) further employed asymmetric microelectrodes for simultaneous pumping and mixing within microfluidics, where the efficiency of 94.9% mixing was demonstrated under the flow rate of 0.27 m2/s. Yoon et al. (Yoon, Kim, & Sung, 2008) employed asymmetric electrode arrays to generate pumping and mixing flow modes with 80% efficacy within 350 µm mixing length under the flow rate of 0.01 m2/s. The performance of various ACEO micromixers developed so far is detailed inTable 1 .