Non-equilibrium high-frequency AC electrokineticsfor precise manipulation of fluid flows andsubmicron colloids in micro-devices

• Main Authors: Jie-Tang Wu, 吳傑堂
• Other Authors: Hsien-Hung Wei
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/83119835388238016319

碩士 === 國立成功大學 === 化學工程學系碩博士班 === 95 === This thesis focuses on non-equilibrium, induced-charge electrokinetic flow (ICEO) under high-frequency AC fields and its applications to micromanipulation of fluids and colloids. There are three parts in this thesis. In Part I, we demonstrate a microelongational streaming generated by nonlinear electro-osmosis due to AC polarization. The phenomenon is attributed to the unique rectification mechanism that coordinates three-dimensional flow interactions between adjacent microvortices set by an asymmetric quadrupole electric field. This streaming exhibits a stagnation-point structure with velocity ~ 300 um/s at 100Hz due to Faradaic polarization, but is reversed with slower velocity at 1kHz by Ohmic charging. The measured extensional rate shows a quadratic dependence on the field in line with nonlinear Smoluchowski scale. In Part II, we employ the same electrode system in Part I and examine the ICEO behavior using different DNA solutions. We find that there exhibit a variety of flow structures, depending on the properties of solutions and applied frequencies. In Part III, we report a new electrokinetic scheme capable of trapping and concentrating a trace amount of DNA molecules both efficiently and effectively. It invokes non-equilibrium charge polarization under high-frequency AC fields, creating a nonlinear electro-osmotic flow with the mobility growing linearly with the field and hence rendering response much faster than that under conventional DC fields. With an asymmetric quadruple electrode design, rectified intense converging and focusing streams transform into a robust electrokinetic funnel with a long-range and superfast trapping capability. We demonstrate that DNAs not only are rapidly concentrated into a compact cone within just few seconds, but also are trapped remotely in the form of focused threads that can extend as far as 1mm. More importantly, the concentration can be enhanced by several decades without any continuous DNA feeding. In addition, this funnel is shown to possess a reversible concentration/release switch when successively turning on/off the field. While this long–range funnel is capable of concentrating dilute DNA solutions as low as 10-2 pM, it further offers a potential means for transporting and concentrating biomolecules in a continuous fashion using a microdevices.