Characterizing Near-Wall Electrokinetics of Colloidal Particles

yodammicrofluidic“芯片上的实验室”（LOC）通过将整个分析化学实验室的内容缩小到几平方厘米，彻底改变了基因组学和酶分析。从微流体到纳米流体的缩小需要对界面传输有一个基本的了解，因为在这些尺度下，整个流动将在距离壁面1 ìm的范围内，而表面作用力（如静电）将变得重要。最近，一些研究表明，在亚微米尺度上，无滑移状态被打破。大多数实验研究（例如，微尺度粒子图像测速或ìPIV）使用确定纳米粒子示踪剂速度的技术，并假设示踪剂速度是流体速度。尤达最近表明，ìPIV示踪剂被排除在外，很可能是静电斥力，从第一个100- 150nm靠近墙壁。根据这种不均匀的示踪剂分布对他们的PIV数据进行校正，结果表明管壁和速度梯度没有滑移，与分析预测一致。假设，作为标准，均匀分布的示踪剂给出200 nm的假滑移长度。据我们所知，没有其他实验研究考虑或量化近壁粒子分布或静电力如何影响他们的数据。因此，我们提出了一项基本的，主要是实验的，为期三年的研究，研究悬浮在平面壁面附近的导电溶液中的胶体粒子在外电场下的动力学，适用于各种粒子-溶液-壁面系统。这是一种新的纳米级组装技术的基本模型：利用电动现象来精确操纵和组装悬浮在导电液体中的纳米颗粒；在各种LOC中使用的微尺度电动驱动流和- PIV研究。这项工作的研究目标是：1。开发新的胶体示踪剂，可以进入距离壁面150nm的流动区域，包括壁面edl，并扩展u/nPIV的测量能力和精度，这是领先的微尺度测速技术。了解影响近壁粒子和壁面电荷分布的哪些物理性质对近壁胶体粒子的电动力学影响最大，以及为什么这些性质会产生这样的影响。拟议的研究将建立在pi之间现有的合作基础上，利用Yoda的新型界面诊断和Olesik的新型纳米颗粒和表面化学专业知识。智力优势：这项工作将通过以下方式推进对微流体的认识和理解：-开发颗粒，包括新的碳纳米颗粒，具有良好控制的表面电荷，既可以用作流动示踪剂，也可以用于电动驱动的纳米颗粒组装；-提高微尺度测速技术的准确性和近壁能力-这可以改变关于破坏无滑移条件的辩论；-通过改变近粒子和近壁电荷分布，确定粒子、壁和表面性质如何影响粒子-壁相互作用和动力学。这项研究具有潜在的变革性，因为：-强健、可靠和可扩展的电动驱动纳米级组装方法将改变纳米电子学，并将纳米技术的好处带给公众；-可靠和精确的界面测速技术将有助于开发基于表面力的新技术，以控制和驱动亚微米尺度的流动，并改造纳米流体装置。更广泛的影响：这项工作将支持开发：-高中水平的基于网络的关于电动驱动流基本方面的演示文稿；-为6 -12年级的学生展示微观和宏观尺度流动的不同之处，例如，在微观和宏观生物使用的不同推进方法（扭转与扑动）方面。这两个pi将继续指导来自代表性不足群体的学生，并确保他们的外展活动包括来自这些群体的学生比例很高的学校

CBET-0828782YodaMicrofluidic "Labs on a Chip" (LOC) have revolutionized genomics and enzymatic assays by shrinking the contents of an entire analytical chemistry laboratory down to a few cm2. Shrinking from micro- to nanofluidics requires a fundamental understanding of interfacial transport since at these scales, the entire flow will be within 1 ìm of the wall-and surface (e.g. electrostatic) forces will become significant. Recently, a number of studies have suggested that the no-slip condition breaks down at submicron scales. Most of the experimental studies (e.g., microscale particle-image velocimetry or ìPIV) use techniques that determine the velocity of nanoparticle tracers, and assume that the tracer velocity is the fluid velocity. Yoda has recently shown that are ìPIV tracers excluded, most likely by electrostatic repulsion, from the first 100-150 nm next to the wall. Correcting their PIV data for this non-uniform tracer distribution gives no slip at the wall and velocity gradients in agreement with analytical predictions. Assuming, as is standard, uniformly distributed tracers gives false slip lengths 200 nm. To our knowledge, no other experimental studies have considered or quantified how near-wall particle distribution or electrostatic forces affect their data. We therefore propose a fundamental, mainly experimental, three-year investigation on the dynamics of colloidal particles suspended in a conducting solution near a planar wall subject to an external electric field for a variety of particle-solution-wall systems. This is a basic model of:- new nanoscale assembly techniques that exploit electrokinetic phenomena to preciselymanipulate and assemble nanoparticles suspended in a conducting liquid; and- PIV studies of the microscale electrokinetically driven flows used in a wide variety of LOC.The research objectives of this effort are to:I. Develop new colloidal tracers that access the flow region within 150 nm of the wall-including the wall EDL-and extend the measurement capabilities and accuracy of u/nPIV, the leading microscale velocimetry techniques.II. Understand which physical properties that affect the near-particle and wall charge distributions have the greatest impact on near-wall colloidal particle electrokinetics and why these properties have such an effect.The proposed research will build on an existing collaboration between the PIs, leveraging Yoda'snovel interfacial diagnostics and Olesik's novel nanoparticles and surface chemistry expertise.Intellectual merits: This work will advance knowledge and understanding of microfluidics by:- Developing particles, including new carbon nanoparticles, with well-controlled surface charge that can be used both as flow tracers and for electrokinetically driven nanoparticle assembly;- Improving the accuracy and near-wall capabilities of microscale velocimetry techniques - which could transform the debate on the breakdown of the no-slip condition; and- Determining how particle, wall and surface properties, by changing the near-particle and nearwall charge distributions, affect particle-wall interactions and dynamics.This research is potentially transformative because:- Robust, reliable and scalable methods for electrokinetically driven nanoscale assembly would transform nanoelectronics and bring the benefits of nanotechnology to the public;- Reliable and accurate interfacial velocimetry techniques will help develop new technologies based on surface forces for controlling and actuating flows at the sub-micron scale, and transform nanofluidic devices.Broader impacts: This work will support development of:- High-school level Web-based presentations on basic aspects of electrokinetically driven flow;- Hands-on demonstrations for 6th-12th grade students that show how micro and macroscale flows differ, for example, in terms of the different methods of propulsion (twisting vs. flapping) used by micro- and macro-organisms. Both PIs will continue to mentor students from underrepresented groups, and ensure that their outreach activities include schools with a high fraction of students from such groups