Electrokinetic Phenomena in Microfluidics and Nanofluidics

提出的研究计划是研究几种新的电动力学微流控现象，这些现象对开发用于医疗诊断和食品安全的芯片实验室设备至关重要，包括：(1)水不混溶离子液体（IL）的电渗透流和电泳。由于离子液体的高粘度，需要通过电动力学手段，即电渗透流和电泳，在微通道中输送离子液体。然而，在这方面还没有任何报道。因此，有必要对离子液体的电渗透流动和离子液体液滴在微通道中的电泳运动进行系统的研究。预期的研究结果将为离子液体的电渗透流动和离子液体液滴的电泳运动提供有价值的实验数据，为未来利用离子液体开发微流控芯片实验室技术提供科学依据。(2)非混相离子液体形成Janus液滴的电动力学现象。在本研究中，我们提出在微流控芯片中使用两种不混溶的离子液体来开发一种新型离子液体Janus液滴，并研究离子液体Janus液滴在微通道中的电动输运现象。我们将研究(A)如何控制Janus液滴的大小以及两种离子液体中的一种所占的Janus液滴比例。(B)离子液滴的电泳迁移率。(C)雅努斯液滴的电动力学运动速度与外加电场和两种不混溶离子液体的比例的关系。(D)如何通过微流控芯片中两种不混溶离子液体的大小和比例来分离Janus液滴。(3)带电荷的聚电解质层修饰纳米通道的EOF。为了调节电解液溶液在小纳米通道中的电动力学传输，本研究将研究如何通过一层一层的聚苯乙烯（PB）和硫酸葡聚糖（DS）的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表面带正电，DS表面带负电，可在PDMS表面交替涂覆（即一层带正电的PB层和一层带负电的DS层，依此循环）。我们将研究修饰后的纳米通道形成多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内电渗透流动的影响。我们将检验(A)电解质溶液离子浓度的影响。(B)电解质离子大小的影响。(C)采用电流斜率法在不同涂覆层数的修饰纳米通道中测量电渗透流动（EOF）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.