Abstract
Recently, micro-total-analysis-systems (uTAS) have received a great deal of attention owning to their ability to revolutionize chemical and biological analysis systems by reducing costs, reagent volumes and electrical power consumption. A microfluidic analysis system is a very important subject, and it could contain several microfluidic components such as micropumps, microvalves, micromixers, and microseparators. For micropumps, electrokinetic micropumps are often applied in chemical/bio experiments. The advantages of electrokinetic micropumps over other micropumps are without the moving mechanical parts, with much simpler designs/fabrication, and they could pump the fluids with a wide range of conductivity. However, these electrokinetic micropumps do not effectively prevent the occurrence of electrolytic bubbles even at a low applied ac potential. Therefore, the objective of this research is to develop a bubble-free ac electrokinetic micropump via such an asymmetric capacitance-modulated microelectrode array. This proposed asymmetric modulation design could shift the optimal frequency of maximum velocity to a higher frequency to minimize the electrolysis bubble generation to enhance the performance. The asymmetric capacitance-modulated microelectrodes are made of an interdigitated Al electrode array and part of individual electrode surface is modulated/deposited with SiO2 dielectric layer. The CFDRC simulation results verify that we could control the fluid flow via the proposed designs. The pumping velocity is measured as a function of the applied voltage, the signal frequency, the electrolyte concentration and the thickness of dielectric layer. A maximum velocity is observed up to 290 um/s in 5mM electrolyte with the applied potential of 10 Vpp in our prototype device. Furthermore, a theoretical model incorporating the effect of double-layer relaxation has also been developed to allow a physical understanding of our proposed micropumps. In this research, we describe the design, simulation, fabrication, experimental results and theoretical model to characterize and demonstrate the performance of the proposed bubble-free ac electrokinetic microfluidic pump.