Study About Specific Separation Of Particles By Pulsed Dielectrophoresis

Particle separation technology is ubiquitous in both traditional and high-tech fields.Recently, it is desirable to develop new separation technology because of traditionalmethods are difficult to be transplanted from macroscopic to microscopic areas due tothe restriction of moving components. In micro-scale, ultrasounds, optical tweezersand dielectrophoresis (DEP) are effective control methods by which particles aremanipulated in the contactless and damageless way. In this paper, theoretical analysis,numerical simulation and experiment were conducted to study the pulsed DEP–basedseparation technology.In microflow, one of typical characteristics is low Reynolds number, which meansviscous force is dominant and volume force or inertial force becomes secondary. Itrequires combining some external force and viscous force together to manipulateparticle. Here, DEP force produced by interdigital electrodes (IDEs) located at thebottom of channel was introduced and Stokes force was produced by a steady laminarflow having very low Reynolds number. The separation of the mixture of3μm,5μmand10μm polystyrene microspheres was realized in microchannel and the nonlinearrelationship of DEP force and Stokes force plays a crucial role.In theoretical aspect, the mechanics model of particle immersed in non-uniformelectric field and steady flow field was constructed. Two key points, equilibrium point(ep) and separation point (sp), were defined and suggested to decide the movementpattern of particle. The effects of main factors, such as flow rate, electric potential,pulsing period, duty cycle and electrode asymmetrical ratio, on separation results wereclarified. Considering that the aggregation of particles cluster would happen under vertical electrode model, slanted IDEs were introduced to overcome this shortage.Particle path and separation principle were studied through force analysis andnumerical simulation for different tilt angles of slanted IDEs.The result indicated that it was possible to separate the mixture of3μm,5μm and10μm particles effectively with the proper parameters, such as period, flow rate,electric potential and so on. Meanwhile, the parameters related to different separationsub-regions were found. Especially, in one of sub-regions, it is found that particles withmiddle size (d=5μm) can be picked out in one step. Moreover, under slanted IDEs, wecan extract any kind of target particles from the mixture of3μm,5μm and10μmparticles by choosing suitable range of parameters. The optimal separation appearswhen the tilt angle is between45°and60°.In experimental aspect, slanted IDEs with tilt angle β=60°was designed and themicrofluidic chip was fabricated by photolithography process. The trajectory of3μmand5μm particles under the slanted IDEs was observed and the preliminary separationprocess was verified. The experimental result roughly agrees with numericalsimulation. These works are the foundation to carry out subsequent experiments andmake improvement.In summary, pulsed DEP merges two separation modes, that is, the strength-basedseparation mode (during "on" cycle) and the mobility-based separation mode (during"off" cycle). It can sort out intermediate-sized particles from larger and smallerparticles and also be able to realize adjustable multiplex separation in continuous flow.Therefore, the present method shows better performance than that of traditionalcontinuous DEP, where only binary separation or sequence separation happens.