Electrokinetic Phenomena in Microfluidics and Nanofluidics

本论文的主要研究内容为：（1）电渗流和电泳现象在离子液体（IL）中的应用。由于离子液体的高粘度，需要通过电动方式在微通道中输送离子液体，即，电渗流和电泳。然而，目前还没有这方面的任何工作报道。因此，有必要进行系统的研究，以了解离子液体的电渗流和离子液体液滴在微通道中的电泳运动。本研究的预期结果不仅为离子液体的电渗流和离子液体液滴的电泳运动提供了科学依据，也为今后离子液体微流控芯片实验室技术的发展提供了有价值的实验数据。 (2)不互溶离子液体形成的Janus液滴的电动现象。在本研究中，我们提出了一种新的类型的离子液体Janus液滴，通过使用两个不互溶的离子液体在微流控芯片，研究离子液体Janus液滴在微通道中的电动传输现象。我们将研究（A）如何控制Janus液滴的大小和Janus液滴被两种离子液体之一占据的比例。(B)离子液体液滴的电泳迁移率。(C)Janus液滴的电动运动的速度作为施加的电场和两种不混溶的离子液体的比例的函数。(D)如何在微流控芯片中根据大小和两种不混溶离子液体的比例分离Janus液滴。 (3)用带电的双金属层修饰的纳米通道的光致变色。为了调节电解质溶液在小纳米通道中的电动传递，本研究将研究如何通过使用聚凝胺（PB）和硫酸葡聚糖（DS）的逐层表面涂层来控制通道壁的表面电荷和纳米通道的横截面尺寸。PB具有正表面电荷，DS具有负表面电荷，并且它们可以交替地涂覆在PDMS表面上（即，一个带正电荷的PB层，接着是带负电荷的DS层，等等）。我们将研究修饰纳米通道的多层包覆层和表面电荷的控制因素，以及这些因素对小纳米通道中电渗流的影响。我们将研究（A）电解质溶液的离子浓度的影响。(B)电解质离子大小的影响。(C)通过使用电流斜率法，将在具有不同数量的涂覆层的改性纳米通道中测量电渗流（electroosmotic flow，EEP）速度。

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, including: (1) Electroosmotic flow and electrophoresis of water-immiscible ionic liquids (IL). Because of the high viscosity of ILs, it is necessary to transport ionic liquids in microchannels by electrokinetic means, i.e., electroosmotic flow and electrophoresis. However, there are no any reported works in this regard. Therefore, it is necessary to conduct systematic research to understand the electroosmotic flow of ionic liquids and electrophoretic motion of ionic liquid droplets in microchannels. The expected results of the proposed research will provide not only scientific insight but also the valuable experimental data of electroosmotic flow of ionic liquids and electrophoretic motion of ionic liquid droplets, for future development of microfluidic lab-on-chip technology by using ionic liquids. (2) Electrokinetic phenomena of Janus droplets made by immiscible ionic liquids. In this research, we propose to develop a novel category of ionic liquid Janus droplets by using two immiscible ionic liquids in microfluidic chips, and study electrokinetic transport phenomena of ionic liquid Janus droplets in microchannels. We will investigate (A) How to control the size of the Janus droplets and the proportion of the Janus droplet occupied by one of the two ionic liquids. (B) The electrophoretic mobility of ionic liquid droplets. (C) The velocity of the electrokinetic motion of the Janus droplets as a function of the applied electric field and the proportion of the two immiscible ionic liquids. (D) How to separate the Janus droplets by size and by the proportion of the two immiscible ionic liquids in microfluidic chips. (3) EOF of nanochannels modified with charged polyelectrolyte layers. In order to modulate electrokinetic transport of electrolyte solutions in small nanochannels, this research will examine how to control the surface charge of the channel wall and the cross-section size of nanochannels by using layer-by-layer surface coating of Polybrene (PB) and Dextran sulfate (DS). PB has positive surface charge and DS has negative surface charge and they can be coated on the PDMS surface alternatively (i.e., one positively charged PB layer followed by a negatively charged DS layer, and so on). We will investigate the controlling factors of building multiple coated layers and surface charges of the modified nanochannels, and the effects of these factors on the electroosmotic flow in small nanochannels. We will examine (A) the effects of ionic concentration of the electrolyte solution. (B) the effects of ion size of the electrolytes. (C) the electroosmotic flow (EOF) velocity which will be measured in the modified nanochannels with different numbers of the coated layers by using the current-slope method.