The integration of micro/nanofluidic devices led to many interesting phenomena and one of the most important and complex phenomenon among them is concentration polarization. In this thesis, we provide new physical insights in micro/nanofluidic interface devices on the application of AC and DC electric fields. By performing detailed numerical simulations based on coupled Poisson, Nernst???Planck, and incompressible Navier???Stokes equations, we discuss the electrokinetic transport and other hydrodynamic effects under the application of combined AC and DC electric fields for different nondimensional EDL thickness and nanochannel wall surface charge density. We understand that for a highly ion???selective nanochannel, the application of combined AC/DC electric field, at amplitudes greater than the DC voltage and at low Strouhal number, results in large dual concentration polarizationregions (with unequal lengths) at both the micro/nanofluidic interfaces due to large andunequal voltage drops at these junctions. The highly nonlinear potential distribution gives rise to an electric field and body force that changes the electrokinetic fluid velocity from that obtained on the application of only a DC source. With the understanding of nonlinear electrokinetic transport under combined AC/DC fields, we propose a novel technique of increasing the product concentration of an enzymatic reaction inside the nanofluidic channel.
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