Research On Electrosmosis Microflow Pumping And Related Technologies

Microfluidics system developed on 1990s is a technology that has emphasis on micro-total-analysis-system (μ-TAS) and lab on a chip based on chemical analysis and biological analysis. It is fabricated on MEMS technology and characterized by microchannel net. Its performance is determined by the key technology of microflow pumping. Despite of the rapid development of microflow pumping technology in the past more than ten years, there are still weakness which limit the application of the microfluidics system, such as the difficulties of systematic integration and the low reliability of the system. To overcome these shortcomings, AC elctroosmosis (ACEO) technology has been developed in recent years for its advantages such as low driving voltage, simple fabrication process and facility of integration with system. Currently, the research of ACEO is at developing stage abroad, while there are few publications have been found in China. Therefore, it is of great significance to research microflow pumping with ACEO.In the study, the theory and the mechanism, as well as the similarity and main features, of ACEO and DC electroosmotic (DCEO) were analyzed. With the design and the test of capillary DCEO pump, the driving voltages and microchannel structures impacting on pumping velocity of DCEO were investigated. In ACEO, the double electric layer is caused by electrode polarization. The velocity formula on ACEO was deduced from the comparison of the mechanism of ACEO and DCEO.In the study of asymmetry ACEO, the physical model of electric field and flow field was proposed based on ACEO pumping microflow experimental phenomenon. The electric and velocity fields with their boundary conditions were analyzed in the simulation. By comparing experimental and simulated results of velocity field of ACEO microflow pumping simulation, the theoretical model was verified.A new idea for the research of traveling wave electromosis (TWEO), that is, a new driving circuit for the chip used in a symmetry electrode array, was presented. The applications of particle image velocity (PIV) method for the measurement of velocity of moving particles and the method of image processing in ACEO and TWEO were discussed. According to the experimental and practical uses, the fabrication processes for ACEO and TWEO chip were compared. Under equivalent driving voltages, the experiments for ACEO and TWEO were studied. The results shows that compared with ACEO, TWEO was more efficient in driving particles. The nonlinear model of voltage distribution for TWEO pumping microflow was presented based on Gouy-Chapman-Stern double electric layer theory. With linear transform, TWEO was simulated. The Poiseuille flow in a closed microchannel was analyzed. The theoretical model of TWEO pumping microflow was verified experimentally. The simulated results show that the streamline of TWEO is smoother than that of ACEO.The factors that influencing characteristics of TWEO microflow pumping were explored experimentally and theoretically. The method for the determination of capacitance ratio coefficients in TWEO with different conductivity of solutions was proposed. Furthermore, the chip electrode fabrication process was shown. The selections of material for chip electrode, substrate and channel were discussed. The experimental results of pumping different conductivity solution show that for lower conductivity electrolyte, the bigger the peak velocity value is, the smaller the frequency for peak velocity is. It is concluded from experimental and theoretical analysis that the variation of structural parameters of electrode may change the electroosmosis velocity and the frequency on peak velocity value. For a low voltage, the effect of electrothermal, particle dielectrophoresis motion and other several factors on the measurement of flow velocity in TWEO microflow pumping can be ignored.On the above discussion, with the basis theory and technology of electroosmosis microflow pumping in this research, ACEO application in engineering has more advantages than DCEO, such as low voltage, facility of integration. Theoretical and experimental research results show that TWEO is more efficiency than ACEO. The experimental and theoretical results are beneficial to the practical application of electroosmosis microflow pumping.The study is sponsored by the Chinese 111 project (Grant Number: B07018) and China Scholarship council"National Project for Sending Graduated Students to Build High Level Universities"(Grant Number: [2007]3020).