Electrohydrodynamic surface microvortices for mixing and particle trapping

We report a free-surface electrohydrodynamic flow phenomenon driven by an ionic wind mechanism induced by a high frequency gas-phase ac field (> 10 kHz). Intense vortices > 1 cm/s are generated above a critical voltage, beyond which the vortices break down to spawn off new vortex pairs leading to a cascade of vortices over a continuum of length scales; the mixing efficiency approaches a turbulent-like state. Colloidal particles are attracted and aggregated into planar crystal structures within the vortices by a combination of dielectrophoresis and shear-induced diffusion. (c) 2006 American Institute of Physics.