Electrokinetic Phenomena in Microfluidics and Nanofluidics

该研究计划旨在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实验室设备至关重要，包括：(1)不溶于水的离子液体(IL)的电渗流和电泳法。由于离子液体的高粘度，离子液体在微通道中的传输需要电动力学方法，即电渗流和电泳法。然而，目前还没有关于这方面的任何报道。因此，有必要对离子液体的电渗流和离子液体液滴在微通道中的电渗运动进行系统的研究。该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渗流和电泳性运动提供了有价值的实验数据，也为未来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)不相容离子液体形成的Janus液滴的电动现象。在这项研究中，我们建议在微流控芯片中使用两种不相容的离子液体来开发一种新型的离子液体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液滴的大小和两种离子液体中的一种占据Janus液滴的比例。(B)离子液体液滴的电泳性。(C)Janus液滴电动运动的速度与外加电场和两种不相容离子液体的比例有关。(D)如何按微流控芯片中两种不相容的离子液体的大小和比例分离Janus液滴。(3)带电聚电解质层修饰的纳米通道的EOF。为了调节电解质溶液在小的纳米通道中的电动传输，本研究将研究如何利用聚布林(PB)和葡聚糖硫酸盐(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表面带正电荷，DS表面带负电荷，它们可以交替地涂覆在PDMS表面(即，一个带正电荷的PB层和一个带负电荷的DS层，以此类推)。我们将研究构建多层涂层和修饰纳米通道的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。我们将考察(A)电解液离子浓度的影响。(B)电解液离子大小的影响。(C)用电流斜率法测量具有不同涂层层数的改性纳米通道中的电渗流速度。

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.