Analysis Of Electroosmotic Flow With Linear Variable Zeta Potential

Micro-Electro-Mechanical System is an integration of mechanical elements, sensors, actuators and electronics on a common chip through microfabrication technology. MEMS promises to revolutionize nearly every product category by bring together silicon-based microelectronics with micromachinging technology, making possible the realization of complete systems on a chip. MEMS is an enabling technology allowing the development of smart products, augmenting the computational ability of microelectionics with the perception and control capabilities of microsensors and microactuators and expanding the space of possible design and applications. The application of microfluidic chip to the separation of batch samples, especially to the Plan of Genomics and the Protenomics, is more and more wide due to its many merits such as promptness, efficiency, delicacy and little consumption in the field o biomedicine. A great deal of manpower and material resources has been plunged into MEMS research in order that the governments can obtain the greatest benefits. Starting with the basic theories of microfluidic, this paper focus on the analysis of electroosmotic flow with linear variable zeta potential, and a rounded theoretical and computational method about the characteristics of electroosmosis between two parallel plates, based on the development of research on the electrokinetic phenomena. As one of the fundamental theory, this study will fasten the research pace of MEMS in china. The main contents are following: The characteristic of electroosmotic flow is presented at first. Being one of the electrokinetic phenomena, when a electric field is applied parallel to the surface, a body force, the interaction between the charge density and the applied electrical potential field will induce the motion of fluid, i.e. the EOF. Compared with the parabolic shape in the traditional pressure-driven flow, the shape of the electroosmotic velocity profile in the fully developed region is flat. As a result, the width sample section is not increased. The control of electroosmosis can be taken by the means of transformation of surface charge and changing the viscosity of the fluid. It is found that the essence of the zeta potential effect on the feature of EOF is significant and clear. In general, zeta potential not only is very important in representing the electrokinetic phenomena but also play a main role in the theory of EDL. When the characteristic size decreases to the level of micron or even nanameter, the influence of EDL on the flow becomes obvious due to scaling effect, surface effect and micro-friction effect. Though micro-law is still functional in solving the problem, modeling the EDL( electrical double layer) theory is more important than it. It is known that most solid surfaces carry electrostatic charges, i.e. an electrical surface potential. If the liquid contains a very small number of ions, the electrostatic charges on the non-conducting solid surface will attract the counterions in the liquid. The rearrangement of the charges on the solid surface and the balancing charges in the liquid is called EDL. The earliest EDL model proposed by Helmholtz is similar with that of slab capacitor, which can't explain the Electrokinetic phenomena and represent the experiment. Then the Gouy-Chapman model is classical diffused EDL model whose key standpoint is that some counterions next to the solid surface are strongly attracted to the solid surface and are immobile, the other counterions diffuse from the slip surface the bulk liquid. The most useful EDL model among these models is the one put forward by Stern, which includes two layers: compact layer and diffuse layer. Moreover, laying emphasis on the asymmetric distribution of charge, Grahame set up the detailed EDL model which comprise inner Helmholtz layer, outer Helmholtz layer and diffuse layer. The electroosmotic flow induced by an applied potential through microchannels between two parallel plates is analyzed in this study. A 2D...