Electrokinetic Phenomena in Microfluidics and Nanofluidics

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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.