Electrokinetic Microfluidics

拟议的研究计划是为了研究几种新的电动微流控现象，这些现象对于开发用于医疗诊断和食品安全的芯片上实验室设备至关重要。所提出的研究计划将：*(1)开发一种基于诱导电荷电渗流的新型微泵。这种新型泵浦是通过在微通道壁上嵌入一对小金属板，并通过靠近金属板的两个电极施加微小的电势差来实现的。外加的局部电场将在金属板上诱导出强烈的电渗流，从而泵送液体。这种泵可以安装在微通道中的任何位置，并且不需要沿整个通道的大电势差(从而避免焦耳加热和对生物细胞的损害)。将开展广泛的理论和实验研究来检验和验证所提出的方法，并将开发此类泵的工作原型。*(2)研究介质极化率对微通道中诱导电荷电渗流(ICEOF)的影响。到目前为止，由于简单，几乎所有对ICEOF的研究都局限于全极化(即金属)材料。然而，微流控应用中的大多数材料都不是完全可极化的；它们是玻璃和聚合物等介电材料。介质的感应表面电势是影响ICEOF的关键因素。本研究的目的是找出感应电荷表面电势与外加电场、固体及其周围液体的极化率之间的关系。将进行广泛的数值模拟和实验验证。本文提出的基础性研究是该领域的首次，将为控制微流控芯片中介电粒子的运动和分离不同类型的介电粒子提供新的认识和方法。(3)研究电诱导Janus液滴的流场和运动。由于液滴的表面电荷是移动的，因此由于外加电场的吸引，表面电荷可以被拉到液滴表面的一侧。这将导致电诱导Janus液滴(EIJD)，即液滴表面一侧带静电的液滴；液滴表面的另一侧没有或很少带静电。这项研究工作将研究(A)电场作用下液-液界面上可移动表面电荷的重新分布；(B)电液界面周围的流场和电液界面在电场中的运动。在本研究的基础上，我们将进一步研究如何控制EIJD的运动，至少有两个应用：由EIJD控制的微流控阀门，以及不同EIJD的分离。

The proposed research program is to investigate several new electrokinetic microfluidic phenomena critical to the development of lab-on-a-chip devices for applications in medical diagnosis and food safety. The proposed research program will:****(1) Develop a novel micro-pump based on induced charge electroosmotic flow. This new pump is realized by embedding a pair of small metal plates on microchannel walls, and applying a small electrical potential difference via two electrodes placed close to the metal plates. The applied local electrical field will induce a strong electroosmotic flow over the metal plates and hence pump the liquid. Such a pump can be installed at any position in a microchannel, and does not require large electrical potential difference along the whole channel (thus avoiding Joule heating and damage to biological cells). Extensive theoretical and experimental studies will be carried out to examine and verify the proposed method, and working prototypes of such pumps will be developed.****(2) Study effects of dielectric polarizability on induced charge electroosmotic flow (ICEOF) in microchannels. So far, almost all studies of ICEOF are limited to fully polarizable (i.e., metal) materials due to simplicity. However, most materials involved in microfluidic applications are not fully polarizable; they are dielectric materials such as glass and polymers. The induced surface potential of dielectrics is critical to the ICEOF. The objective of this research is to find the correlation of the induced charge surface potential to the applied electrical field, the polarizability of the solid and its surrounding liquid. Extensive numerical simulations and experimental verifications will be conducted. This proposed fundamental research is the first in this field, will provide new understanding and develop new methods to control the motion of dielectric particles and to separate different types of dielectric particles in microfluidic chips.****(3) Study the flow field and motion of electrically induced Janus droplets (EIJD). As the surface charges of the droplet are mobile, the surface charges can be pulled to one side of the droplet surface due to the attraction to the applied electrical field. This will result in an electrically induced Janus droplet (EIJD), a droplet with electrostatic charges on one side of the droplet surface; the other side of the droplet surface has no or little electrostatic charges. The proposed research work will study (a) the redistribution of mobile surface charges of liquid-fluid interfaces under the influence of electrical field; (b) the flow field around an EIJD and the motion of EIJD in an electric field. With the fundamental understandings developed from this study, we will further study how to control of EIJD motion for at least two applications: a microfluidic valve controlled by EIJD, and separation of different EIJDs.***