Control of two-phase flow in microfluidics using out-of-phase electroconvective streaming

Abstract

We propose herein to make use of rotating electric fields for achieving flexible control on the hydrodynamic behavior of two miscible co-flowing water solutions in straight microchannels, in the context of a new manipulation tool for stratified liquid contents of microfluidic systems. Our theoretical analysis indicates that, while fluids of distinct electrical conductivities and identical permittivity are parallel pumped into the mainchannel, a circularly traveling field, as emitted from a four-phase electrode array surrounding the channel sidewalls, can direct the deflection of diffusing phase interface between the side-by-side miscible electrolyte streams asynchronously at half of the interfacial relaxation frequency, where the co-field electrorotational torque becomes most appreciable. An immediate application of the out-of-phase electroconvective streaming is that time required for electrolyte mixing is reduced because the area of two-phase contact interface is dramatically enlarged, and a serial combination of several rotating electrode arrays of alternate propagating directions can further rectify the mixing of microfluidics by inducing chaotic advection.