Effects of multiple electrode pairs on the performance of a micromixer using dc-biased ac electro-osmosis

Recently, ac electro-osmosis (ACEO) has attracted intensive attention due to its capabilities of pumping and mixing enhancement with relatively low voltages. In this paper, we report the effects of electrode arrangement on the performance of a micromixer using dc-biased ACEO with respect to flow rate and ac frequency. The mixer consists of two inlet channels and a straight main microchannel with gold electrode pairs deposited on its bottom, and utilizes asymmetric vortex flows generated by dc-biased ACEO for mixing. The results indicate that there is significant dependence of mixing performance on the number of electrode pairs, especially for different flow rates. For example, the single electrode pair resulted in the best mixing performance at the highest flow rate of 9 mu L min(-1) (average velocity of 2.5 cm s(-1)) while three or four electrode pairs provided the maximum mixing performance for the flow rate lower than 4 mu L min(-1) (4.11 cm s(-1)). Also, we found that a mixing index of 95% can be achieved by using three electrode pairs while a single electrode pair leads to a mixing index of 85% for a given condition.