Particle Electrokinetics in Non-Newtonian Microfluidics

在过去的二十年里，微流控器件在许多化学、生物医学和环境应用中得到了越来越多的应用。许多应用需要精确放置和运输颗粒(从大分子到病毒和细胞，从胶体到珠子等)。在微通道中。电场的应用是控制微流控系统中颗粒运动的首选方法，因为它具有操作简单、精确度高、操作自主性以及与其他分析组件集成的优点。电场可以引起带电粒子的运动(电泳法)或周围流体的运动(电渗法)。这种所谓的电动粒子运动已经在简单液体中得到了广泛的研究。然而，它在聚合物溶液、胶体溶液、生物流体等复杂流体中还没有得到广泛的研究，这些流体都是非牛顿流体的例子，在流动中表现出不寻常的性质。本项目的目标是发展有关聚合物溶液中通过微通道的电动粒子运动的基础知识。这项研究将消除流体弹性和剪切稀化效应对通道轴方向的电泳运动和颗粒向通道壁侧向迁移的影响，以找到控制颗粒运动的方法。这些实验将扩展到尚未被考虑用于非牛顿流体系统的大电场。这项研究将被紧密地编织到克莱姆森大学的本科生和研究生课程中，并将成为南卡罗来纳州为高中生开发的活动的基础。本科生和高中生，特别是那些来自代表性不足群体的学生，将通过系、大学和州政府提供的各种项目积极参与该项目。该项目将是通过微通道在非牛顿流体中电动粒子运动的第一个全面研究。在(1)纯直流电场、(2)压力梯度直流电场和(3)高达1 mV/m(比典型电动微流体高一个数量级)的纯交流电场作用下，对聚合物溶液在矩形直微通道中的轴向运动和横向运动进行了系统的实验研究。五种具有不同流变性的常见聚合物溶液将被测试，并与牛顿流体进行比较。这些实验将单独和联合研究流体弹性和剪切稀化对电泳液颗粒的线性和非线性运动以及伴随而来的横向颗粒迁移的影响。粒子迁移率和迁移的实验数据将与理论公式和数值模拟的预测进行比较，如果有的话。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Microfluidic devices have been increasingly used over the past two decades for numerous chemical, biomedical and environmental applications. Many applications require precise placement and transport of particles (ranging from macromolecules to viruses and cells, from colloids to beads, etc.) in microchannels. The application of an electric field is the method of choice to control particle motions in microfluidic systems because of the ease, precision, autonomy of operation and integration with other components for analysis. The electric field can induce motion of a charged particle (electrophoresis) or the motion of the surrounding fluid (electroosmosis). This so-called electrokinetic particle motion has been extensively studied in simple liquids. However, it has not been studied extensively in complex fluids such as polymer solutions, colloidal solutions, biological fluids, which are examples of non-Newtonian fluids that exhibit unusual properties in flow. The goal of this project is to develop a fundamental knowledge of electrokinetic particle motion in polymer solutions through microchannels. The research will delinate effects of fluid elasticity and shear-thinning effects on electrophoretic motion in the direction of the channel axis and lateral migration of particles toward the channel walls in order to find ways to control particle motions. The experiments will be extended to large electric fields that have not yet been considered for non-Newtonian fluid systems. The research will be intimately weaved into undergraduate and graduate curricula at Clemson University and will form the basis for activities developed for high school students in South Carolina. Undergraduate and high school students, especially those from underrepresented groups, will be actively involved in the project through various programs available in the department, university, and state.This project will be the first comprehensive study of electrokinetic particle motion in non-Newtonian fluids through microchannels. A systematic experimental investigation of both the axial motion and lateral migration of particles will be performed in the flow of polymer solutions through straight rectangular microchannels under (1) pure DC electric field, (2) DC electric field imposed with a pressure gradient, and (3) pure AC electric field with a magnitude of up to 1 MV/m (one order of magnitude higher than in typical electrokinetic microfluidics) in each case. Five types of common polymer solutions with distinct rheological properties will be tested and compared against Newtonian fluids. The experiments will investigate effects of fluid elasticity and shear thinning, individually and in combination, on the linear and nonlinear electrophoretic particle motions as well as the accompanying lateral particle migration. The experimental data of particle mobility and migration will be compared with the predictions of theoretical formulae and numerical simulations, if available.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.