Characterizing Near-Wall Electrokinetics of Colloidal Particles

CBET-0828782优达微流控芯片实验室(LOC)通过将整个分析化学实验室的内容缩减到几平方厘米，彻底改变了基因组学和酶分析方法。从微米流体到纳米流体的收缩需要对界面传输有一个基本的了解，因为在这些尺度下，整个流动将在壁面的1？m以内-表面(例如静电)力将变得很大。最近，一些研究表明，防滑条件在亚微米级就失效了。大多数实验研究(例如，微尺度粒子图像测速仪或？PIV)使用确定纳米粒子示踪剂速度的技术，并假设示踪剂速度为流体速度。尤达最近证明，在靠近墙壁的第一个100-150 nm范围内，PIV示踪剂被排除在外，这很可能是由于静电排斥。根据这种不均匀的示踪剂分布对他们的PIV数据进行修正，在壁面和速度梯度处没有滑移，与分析预测一致。按照标准，假设均匀分布的示踪剂给出的假滑移长度为200 nm。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，我们提出了一项为期三年的基本的、主要是实验的研究，以研究各种颗粒-溶液-壁系统在平板外电场作用下，悬浮在导电溶液中的胶体颗粒的动力学。这是一个基本模型：-新的纳米级组装技术，利用电动现象精确地操纵和组装悬浮在导电液体中的纳米颗粒；这项工作的研究目标是：I.开发新的胶体示踪剂，以访问壁面150 nm以内的流动区域--包括壁面EDL--并扩展领先的微尺度测速技术u/nPIV的测量能力和精度。ii.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电动力学的影响最大，以及为什么这些性质具有这种影响。拟议的研究将建立在PIs之间现有的合作基础上，利用Yoda的新界面诊断和Olesik的新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提高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，既可用作流动示踪剂，也可用于电动驱动纳米颗粒组装；-提高微尺度测速技术的准确性和近壁能力--这可能改变关于防滑条件崩溃的争论；以及-通过改变近颗粒和近壁电荷分布，确定颗粒、壁面和表面性质如何影响颗粒-壁面相互作用和动力学。这项研究具有潜在的变革性，因为：-用于电动驱动纳米尺度组装的健壮、可靠和可扩展的方法将改变纳米电子学，并将纳米技术的好处带给公众；-可靠和准确的界面测速技术将有助于开发基于表面力的新技术，用于在亚微米级别控制和驱动流动，并改变纳米流体设备。广泛影响：这项工作将支持以下开发：-关于电动驱动流动的基本方面的高中水平的网络演示；-面向6-12年级学生的动手演示，展示微观和宏观尺度流动的不同之处，例如，微型和宏观生物体使用的不同推进方法(扭动和拍打)。这两个私人助理将继续指导来自代表不足群体的学生，并确保其外展活动包括来自这类群体的学生比例较高的学校

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