Electrohydrodynamic Flow for Microfluidic Mixing and Microparticle Manipulation

We discuss the mechanisms by which bulk electrohydrodynamic air thrust or ionic wind generated above and directed towards the surface of a microfluidic chamber by a sharp electrode tip can give rise to surface or bulk liquid recirculation in the chamber and demonstrate various ways in which the phenomenon can be exploited for microfluidic mixing and particle trapping. In the latter, microparticles are either rapidly concentrated due to the primary azimuthal surface vortices into planar crystal aggregates or spun down in a helical swirl-like fashion to a bottom central stagnation point by the bulk meridional rotational flow. In particular, we show that this is a useful mechanism for separating red blood cells from blood plasma for miniature point-of-care diagnostic kits.