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Multiphysical Modeling of DC and AC Electroosmosis in Micro- and Nanosystems

出版	INTECH Open Access Publisher, 2008
主題	Computers / Computer Simulation
ISBN	39026132549783902613257
URL	http://books.google.com.hk/books?id=CDfooAEACAAJ&hl=&source=gbs_api

註釋The described Poisson-Nernst-Planck-Navier-Stokes nonequilibrium mathematical model is a powerful tool for analysis of the reaction transport processes in various microfluidic devices, namely, geometrically complex microfluidic structures with polarizable dielectric walls or deposited metal electrodes with an imposed electric potential under the electrochemical limit. The microfluidic structures have to be filled with a liquid electrolyte, no electrochemical interactions have to occur, and the applications have to be performed under isothermal conditions. For example, the proposed mathematical model enables numerical analysis of: (i) chemical and biochemical interactions in homogeneous and heterogeneous arrangement, (ii) the combined diffusion-electromigration-convective transport of ionic and electroneutral components, (iii) the DC electroosmotic convection induced at polarized surfaces, (iv) the AC electroosmotic convection forced at microelectrode arrays, (v) the pressure and the velocity fields etc. It has been demonstrated that the use of the nonequilibrium model is necessary, e.g., when the characteristic dimension of the microfluidic device is comparable with the thickness of EDL (low concentrated electrolytes, very thin microchannels) or the polarized dielectric walls interact with an ionic reaction components diluted in the electrolyte. We have shown that a porous structure surrounded by an aqueous electrolyte and affected by an external DC electric field can behave as either a DC micropump or an ionexchange membrane. The behavior depends on the pore diameter, the electrolyte concentration and other parameters. Interesting nonlinear hydrodynamic phenomena such as the eddy formation were observed in our simulations. In the future, our work will deal with the analysis of complex electrohydrodynamic processes in the pores and the surrounding electrolyte in the overlimiting current domain. It can contribute to the overlimiting current theory. Selected characteristics of the AC electroosmosis forced by the coulombic force in the studied microchannels have been presented. Both asymmetric (interdigitated) and symmetric (traveling wave) arrangements were analyzed by means of the nonequilibrium model. The obtained characteristics are nonlinear and the explanation of the flow reversals remains unclear, except the finding that the flow reversals do not necessarily rely on the electrochemical reactions. However, the model gives us the opportunity to get not only qualitative but also quantitative insights into flow reversals via detailed analysis of spatiotemporal fields of all dependent variables.