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

Abstract

A large family of microfluidic devices employs the electrokinetic transport of liquids. The integration of mechanical components such as high-pressure pumps or valves is not required in the electrokinetically driven microfluidic chips. Instead of a pressure gradient, a gradient of electric potential is imposed over the microfluidic system. It can be provided by either DC or AC electric field. The DC electroosmotic transport in microchannels has been intensively theoretically and experimentally studied. The origin of the DC electroosmosis arises from the coulombic interaction between an external DC electric field and a mobile electric charge localized at an electrolyte-dielectric interface. The use of the electroosmosis forced by a low amplitude AC electric field is a novel area investigated only for several years. The AC electroosmosis is mostly based on the coulombic interaction between an imposed AC electric field and a mobile electric charge temporally arising at electrolytemetal electrode interfaces. The chapter is organized as follows. The origin of the electrokinetic transport and the principle of DC and AC electroosmotic micropumps are shortly described in the first section. The basic features of the AC micropumps are summarized in more detail. The multiphysical model of electro-microfluidic systems based on the Poisson-Nernst-PlanckNavier-Stokes approach and its possible simplifications are briefly described in the second section. The implementation procedure of this multiphysical problem in a CFD software and frequently arising problems are discussed in the next section. Various electro-microfluidic systems have been investigated in our research group. Here, we present and discuss selected results of the numerical analysis of three particular microand nano-fluidic systems: (i) a tubular microfluidic sensor for heterogeneous immunoassay driven by a DC electric field, (ii) a submicron channel/pore interacting with a DC electric field and the surrounding electrolyte, (iii) AC electrokinetic microand nano-pumps realized in channels with spatially periodic arrays of co-planar electrodes. The discussed AC pumps rely either on the asymmetric geometry of interdigital electrodes or on an electric field phase shift applied to electrodes (the three phase arrangement).