Magnetic field-controlled microfluidic transport

Several new forms of magnetohydrodynamic (MHD) flow occurring in the solution gap between two 250-mum-diameter Pt microdisk electrodes, oriented in a face-to-face geometry and immersed in a uniform magnetic field (1 T), are described. The MHD flow results from the Lorentz force generated by diffusion of electrochemically generated molecular ions through the magnetic field. Individual microscopic flow tubes (similar to50-mum radius) spanning the gap between the face-to-face electrodes are observed during the 1-e(-) reduction of nitrobenzene in acetonitrile solutions. The flow tubes extend up to similar to2 cm in length and are stable for indefinite periods. Directional transport of the electrogenerated nitrobenzene radical anion over macroscopic distances within the flow tubes, with minimal diffusional broadening, is demonstrated using an ultramicroelectrode probe to map the convective flux of redox species, Pulsed MHD transport of small packets of molecules and the formation of large area (similar to3 cm(2)), microscopically thin (25 mum) rotating sheets of solution are also demonstrated. The results suggest that electrochemical methods, in combination with magnetohydrodynamic principles, may be useful for external field-controlled microfluidic systems.