Faradaic Micro-Fluidic Devices for Complex Fluids

将研究一种在微流控装置中输送、计量、控制、分离和浓缩液体和生物颗粒的新的电动方法。与现有的直流(DC)和交流(AC)电动技术不同，这种法拉第交流电动(FACE)机制通过瞬时法拉第电极反应，在微细加工电极上产生大的准平衡极化，以超过1厘米/S的速度驱动微通道中的流体和颗粒运动，是最强大的非机械式微泵之一。由于采用了高频(100 KHz)交流电场，瞬变反应不会在微通道中产生气泡和离子污染物。它对DNA、蛋白质和生物粒子的破坏也不像直流场那么大。观察到了各种新的单相和多相电动现象，它们具有本质上不同的流动拓扑和不稳定性。流动拓扑的丰富性归因于两种基本的法拉第极化机制，这两种机制产生了局域压陷和切向滑移速度。拟议的项目将对这一新的电动机制进行基本分析，并描述/量化其各种流动特性。这项基础性研究将使我们能够基于这一新机制，有时通过利用新现象来优化微流控部件的设计。这些研究包括匹配的渐近分析，用时间平均的有效静电和滑移边界条件来代替纳米级双层内的快速(US)反应和电容充电动力学，从而简化了相关的多尺度数值研究。还将分析几何奇异点的切向传导和电荷积累，这被认为是驱动一些异常流动的原因，以全面描述复杂的时空电极极化动力学。强流提供的高剪切速率导致了许多生物颗粒的分离和聚集现象，我们将对此进行详细的研究，以制定有效的颗粒-流体分离策略，为荧光标记检测提供生物颗粒和病毒。微细加工的交流电磁铁将产生横向洛伦兹力，以产生螺旋流以及电流涡流和线形面流。拟议的基础性工作将使我们能够有效地理解和利用这种新的表面机制，以构建具有优化的电极几何和施加电场的功能微流控技术。教育影响：拟议的工作将为研究生提供异常丰富的教育经验。它将对新物理现象的基础科学研究与工程设计项目结合起来，生产出几乎可以商业化的微流体设备。它涉及复杂的理论和数值分析，以及最先进的制造技术。在过去的四年里，我们的实验室在美国主要研究型大学安排了5名小组成员担任终身教职，两名成员在领先的工业研究中心，两名本科生成员在顶尖研究生项目。其他四人将很快寻求终身教职。我们预计拟议的项目将产生类似的教育影响。科技影响：最近在病毒检测、细菌检测、化学色谱等芯片规模分析技术方面的基础科学研究已经并将继续推动医疗、环境和国家安全行业的重大技术进步。仍在开发中的一个主要组件是微流控技术：能够精确地运输、混合和操纵流体，更重要的是，能够在芯片微通道内传输微米和纳米级的生物颗粒。电动力学是一种利用成熟的微加工技术嵌入微电极来制备理想的微流体的方法。该项目研究了一种新的电动机制，该机制由该小组首次揭示，有望比其他微流体组件更强大、更可靠和更灵敏。所提出的工作将为基于这一新机制的第一个功能性微流控部件奠定基础。

ABSTRACT - 0454956A new electro-kinetic means of transporting, metering, controlling, separating and concentrating liquid and bio-particles in a micro-fluidic device will be investigated. Unlike existing direct-current (DC) and alternating-current (AC) electro-kinetic techniques, this Faradaic AC Electro-kinetic (FACE) mechanism produces large quasi-equilibrium polarization of microfabricated electrodes via transient Faradaic electrode reactions to drive fluid and particle motions with speeds in excess of 1 cm/s in micro-channels, representingone of the most powerful nonmechanical micro-pump. Due to the high-frequency ( 100 kHz) AC field employed, the transient reactions do not produce bubbles and ionic contaminants in the micro-channels. It is also not as damaging to DNA, proteins and bio-particles as DC fields. A variety of new single-phase and multi-phase electro-kinetic phenomena, with qualitatively different flow topologies and instabilities, have been observed. The richness of the flow topologies is attributed to two fundamental Faradaic polarization mechanisms that generate a localized pressure sink and a tangential slip velocity. The proposed project will carry out a fundamental analysis of this new electro-kinetic mechanism and delineate/quantify its various flow properties. This fundamental study will allow us to optimize the design of micro-fluidic components based on this new mechanism, sometimes by harnessing the new phenomena. The studies include a matched asymptotic analysis to replace the fast (us) reaction and capacitive charging dynamics within the nm-sized double layer with time-averaged effective electrostatic and slip boundary conditions, thus simplifying the relevant multi-scale numerical studies. An analysis of tangential conduction and charge accumulation at geometric singularities, which are believed to drive some of the anomalous flows, will also be carried out to fully delineate the complex spatio-temporal electrode polarization dynamics. The high shear rate afforded by the strong flow causes many bio-particle segregation and aggregation phenomena, which will be studied in detail to produce effective particle-fluid separation strategies, bio-particle and virus for fluorescent tag detection. Microfabricated AC electro-magnets will produce transverse Lorentz forces to generate spiral flows as well as the current vortex and linear FACE flows. The proposed fundamental work will allow us to fruitfully understand and exploit this new FACE mechanism to build a functional micro-fluidic technology with optimized electrode geometries and applied electric fields.Educational Impact: The proposed work will provide graduate students with an unusually rich educational experience. It combines fundamental scientific studies of new physical phenomena with engineering design projects to produce nearly commercializable micro-fluidic devices. It involves sophisticated theoretical and numerical analyses, as well as state-of-the-art fabrication technology. In the last four years, our laboratory has placed 5 group members in tenure-track faculty positions at major U.S. research universities, two in leading industrial research centers and two undergraduate members at top graduate programs. Four others will be seeking tenure-track positions shortly. We expect the proposed project to make a comparable educational impact.Scientific and Technological Impact: Recent fundamental scientific research on chip-scale analytical techniques for viral assays, bacteria detection, chemical chromatography, etc. has and will continue to spur a major technological advance in the medical, environmental and national security industries. A major component that is still under development is micro-fluidics: the ability to precisely transport, mix and manipulate fluids and, more importantly, micro- and nanoscale bio-particles within the chip micro-channels. Electro-kinetics is one approach that utilizes mature micro-fabrication technology to imbed micro-electrodes to produce the desirable microfluidics. This project investigates a new electro-kinetic mechanism, first revealed by the group, that promises to be more powerful, reliable and sensitive than other micro-fluidic components. The proposed work will lay the fundamental groundwork for the first functional micro-fluidic components based on this new mechanism.