Mechanism And Experimental Research On Scaled Particle Focusing Utilizing Induced Charge Electroosmosis

The microfluidic system allows a series of reactions to be carried out simultaneously, which are imparted an ascending/descending analyt e concentrations to evaluate the optimal condition. The conventional methods can hardly satisfy the demand of microvolume, so it is necessary to produce discrete concentrations in microfluidic platform. The key component of generating discrete concentrations is to focus particles with scaled numbers. I nduced charge electroosmosis(ICEO) provides a promising method for scaled focusing, since ICEO is proportional to electrode size. The flow field, control mechanism, the geometrical characteristics of the ICEO flow and experimental studies of particle focusing are presented herein.Firstly, a scaled particle focusing method utilizing ICEO has been proposed. Applying an AC voltage source, particles are collected above two parallel floating electrodes of unequal width without the external circuit connection. And there is a focusing-particle number ratio between two columns of particle band.Second, deducing the slip velocity in phasor notation and performing numerical simulations of the ICEO in microchannel, the microvortex formation and asymmetric velocity distribution are revealed, along with a flow stagnation region to trap particles. The response of ICEO to voltage signal is studied, combined with mult iphysic effects, which lead to the proportional focusing model together and an ideal slip velocity profile for particle focusing. By adjusting slip velocity profile close to the ideal one, the operating range of electric voltage signal is selected.Then, starting from the important sizes, building the criterion for vortex actuation range, the geometrical characterist ics of the ICEO flow are obtained, as the theoretical basis of asymmetric electrodes design. Considering the distraction from fabrication and experimental operation, the overall scheme s of microfluidic device are designed, sharing the identical basic asymmetric electrodes. By studying the impact of conductivit y and pressure driven flow, the basic experimental condit ion is determined. In view of the quantities of chip consuming, a new fabrication process is refined, and the manufacturing efficiency is greatly improved.At last, the theoretical model was validated and enhanced by three groups of experiments of static, flow and large span concentration. Static particle trapping confirm the predict ion of the voltage signal operation range, and the validity of the selection of the pressure driven flow is verified by the measurement of the shrink of particle focusing band width. The flow experiments reveal the electric control response of the particle concentrator, which can be used as an actuator. The particle concentrator and counter are able to build a closed loop control system, bringing the benefits of high-accuracy and robustness. The large span concentration experiments have shown the superiorit y of ICEO concentrator in concentration span and number. Therefore, scaled particle focusing utilizing ICEO has promising applications in mult iple reactions and the formation of discrete concentrations.