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23 January 2006 Theoretical and experimental study of electroosmosis-driven two-fluid displacement in a microcapillary
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Fluid flow in microfluidic systems can be achieved by electroosmosis (EO) pumping, with its own unique characteristics and advantages. In practice, multi-fluid (one fluid displacing another fluid) flows are frequently encountered. Understanding of multi-fluid EO flow associated with non-uniform liquid properties is of importance to precise flow control. This paper reports an EO-driven, two-fluid displacement flow in a microcapillary. The electrical current monitoring method is adopted for investigating the dynamic flow response. The nonlinear change of the electrical current with time under a constant applied voltage is observed during the displacing processes. The theoretical and experimental results validate the hypothesis that the non-uniform zeta potential and electric field induce local pressure gradients in the two different fluids. This results in the deviation of the velocity flow profile from the ideal plug-like flow profile expected for EO flow. The model predictions agreed well with the experimental data when a low concentration fluid displaces a high concentration fluid, but not vice versa. The time of displacement, and thus the flow velocity, is found to be dependent on the displacing flow direction, which is hitherto not reported. The underlying mechanisms are postulated, but require further investigation.
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H. Y. Gan, C. Yang, Stephen Y. M. Wan, G. C. Lim, and Y. C. Lam "Theoretical and experimental study of electroosmosis-driven two-fluid displacement in a microcapillary", Proc. SPIE 6112, Microfluidics, BioMEMS, and Medical Microsystems IV, 61120K (23 January 2006);


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