Manipulating Fluid Flow on a Chip through Redox Magnetohydrodynamic Induced Convection

by Weston, Melissa Christine; Fritsch, Ingrid

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Redox MHDs (MHD) can move fluid on a small scale in a soln. contg. redox species through the generation of a Lorentz force that equals the cross product of ion flux produced by oxidn. and redn. at electrodes and a magnetic field. Faradaic current was generated in a soln. contg. electroactive species at microband electrode arrays by application of a potential or current. Although the potential defines the species that oxidize and reduce, the resulting current also depends on the kinetics of the electron transfer and the mass transport of species to the electrode surface. Thus, when the fluid begins to move, the current can also change, resulting in further variation in fluid velocity. Therefore, if a current is applied below the mass-transport limited value, the fluid velocity can readily be controlled. A quant. comparison of the dependence of velocity on potential and current is reported. A small vol. electrochem. cell was constructed over microelectrode arrays and the whole assembly was placed on a permanent magnet. A microscope was used to track movement of microbeads in the electroactive soln. to det. the direction and magnitude of the flow. The effects of electrode size, cell height, and electrode spacing and configuration on spatially distributed velocities will be discussed. Velocity flow profiles throughout the cell and over time are reported. This work may provide insight into the development of redox MHD as a novel microfluidic approach that could complement the characterisitics of other microfluidic pumping methods for lab-on-a-chip devices.