(87b) Improved Mixing in a Pressure Driven Straight Microchannel Using Electroosmosis

We propose a design for improving mixing in the flow of electrolytic solutions in microchannels, through a combination of electroosmosis and pressure driven flow. We show that a secondary flow is induced on application of a transverse electric field. The resulting flow field consists of a pair of helical vortices that transport fluid elements across the channel cross-section. The electroosmotic vortices described here are stronger in smaller channels, due to the increased influence of the electric double layer. We characterize the strength of the circulatory flow as a function of the applied electric field and fluid properties. We then apply this principal to design a straight channel chaotic micro-mixer. Here, we show how chaotic advection may be induced in straight rectangular channels, by applying an electric field whose direction varies periodically along the length. This electroosmotic chaotic mixer has the advantage of efficient and controlled mixing even at low flow rates and small channel dimensions. Moreover, it eliminates the two major drawbacks of active mixing by improving mixing without increasing the pressure drop or requiring moving parts. Extent of mixing is characterized by using Poincare maps, Shannon entropy and species transport equation.