Collaborative Research: Deciphering Induced-Charge Electrokinetics: Multiscale Simulations and Nanoscale Flow Characterization

感应电荷电动力学(IC-EK)是一类源于电场驱动下感应空间电荷在电解液中迁移的输运现象。由于IC-EK在流体/颗粒操纵方面与经典EK相比具有明显的优势，有望给微流控技术带来重大突破。然而，对IC-EK仍然缺乏一个基本的理解：尽管一些实验趋势可以解释，但理论往往高估了实验测量10-100倍，一些观察结果甚至不能定性地解释。这表明，现有的理论中缺少一些重要的物理学。识别和阐明这种物理对于促进对IC-EK的基本了解和最大限度地发掘IC-EK在微流控技术中的潜力具有重要意义。智力价值：这项合作工作的目标是使用交流电渗流(AC-EOF)作为模型问题来研究IC-EK，AC-EOF是IC-EK的代表成员。中心假设是现有理论中对斯特恩层、界面流体流变性、非平衡双电层(EDL)及其与流体流动的耦合缺乏准确的描述，导致实验与现有理论之间的差异。在这一假设的推动下，计划实现两个具体目标：1)开发一种多尺度模拟工具，准确地解释斯特恩层和界面流体的流变性，并显式地解析非平衡EDL和体电解质中的离子/流体动力学；2)通过将多尺度建模与纳米尺度流动表征相结合来阐明AC-EOF的实验异常，并利用本工作中获得的见解探索基于AC-EOF的器件的新设计。计划中的流量测量将解决纳米级非平衡EDL内的流动和电极附近的涡旋动力学。总而言之，这些研究将使AC-EOF实验异常的潜在物理学能够以前所未有的精度被描绘出来。这项研究具有潜在的变革性。首先，本文所获得的见解将为AC-EOF器件的合理设计奠定基础，以克服其局限性。其次，通过阐明界面流体的流变性对电渗流的影响以及非平衡电动力学在AC-EOF中的作用，本研究将极大地推动EK理论的发展。特别是，定量地确认非平衡EDL在AC-EOF中的重要性可能会导致整个IC-EK传输类的理解和控制方式的范式转变。广泛的影响：计划了一系列活动，以鼓励和准备本科生在计算科学和工程领域从事职业。参与这个跨学科项目的学生将接触到不同的领域，如计算电流体力学和界面科学。将利用各种资源，例如私人投资机构的少数族裔招聘/保留方案，从代表性不足的群体中招募学生参加这一项目。这些活动将受益于私人投资经理在这些项目上的经验。研究成果将编成单元，供私人投资主任教授的微米/纳米流体学课程使用。研究成果还将被制作成视频和海报，用于K-12外联活动，并提交给Efluids.com托管的流体运动/图像图库。

Qiao/Wang1336224/1336004Induced-charge electrokinetics (IC-EK) is a class of transport phenomena originating from the migration of induced space charges in electrolytes driven by electrical fields. Because of its distinct advantages over the classical EK in fluid/particle manipulation, IC-EK is expected to bring significant breakthroughs to microfluidic technologies. A fundamental understanding of IC-EK is, however, still lacking: although some experimental trends can be explained, theories often overpredict experimental measurement by 10-100 folds, and some observations cannot be explained even qualitatively. This suggests that some important physics are missing from the existing theories. Identifying and elucidating such physics is important for advancing the basic understanding of IC-EK and for exploring IC-EK's potential in microfluidic technologies to the fullest extent. Intellectual Merit :The objective of this collaborative effort is to investigate IC-EK using alternating current electroosmotic flow (AC-EOF), a representative member of IC-EK, as a model problem. The central hypothesis is that the discrepancy between experiments and existing theories is caused by a lack of accurate account of the Stern layer, rheology of interfacial fluids, non-equilibrium electrical double layers (EDLs), and their coupling with fluid flow in existing theories. Driven by this hypothesis, two specific objectives are planned: 1) to develop a multiscale simulation tool that accurately accounts for the Stern layer and the rheology of interfacial fluids, and explicitly resolves the ion/fluid dynamics in non-equilibrium EDLs and bulk electrolytes; 2) to elucidate the experimental anomalies of AC-EOF by integrating multiscale modeling with nanoscale flow characterization and to explore new design of AC-EOF-based device using the insights gained in this work. The planned flow measurement will resolve flow within the nanoscopic non-equilibrium EDLs and the dynamics of vortices near electrodes. Together, these studies will enable the underlying physics of the experimental anomalies of AC-EOF to be delineated with unprecedented accuracy. The research is potentially transformative. First, the insights gained here will lay foundation for the rational design of AC-EOF devices to overcome their limitations. Second, by elucidating the impact of the rheology of interfacial fluids on EOF and the role of non-equilibrium EDLs in AC-EOF, this study will significantly advance EK theory. In particular, quantitatively confirming the importance of non-equilibrium EDLs in AC-EOF can potentially lead to a paradigm shift in how the entire class of IC-EK transport is understood and controlled.Broader Impacts :A series of activities are planned to encourage and prepare undergraduate students to pursue careers in computational science and engineering. Students participating in this interdisciplinary project will be exposed to diverse fields such as computational electrohydrodynamics and interfacial sciences. Various resources, e.g., the minority recruitment/retention programs at the PIs' institutions, will be utilized to recruit students from under-represented groups to participate in this project. These activities will benefit from the PIs' experience with these programs. Research results will be developed into modules for the micro/nanofluidics courses taught by the PIs. Research results will also be developed into videos and posters for use in K-12 outreach activities and for submission to the gallery of fluid motion/images hosted by Efluids.com.