Investigation of the Zeta Potential of Electrically Polarized Inrterfaces

国家科学基金会-化学和运输系统颗粒和多相工艺计划部门(1415年)提案编号：0730391首席研究员：赛斯，保罗附属公司：卡内基梅隆大学提案标题：调查电极化的Zeta电位界面本研究的领域是胶体颗粒在电极上的电化学定向自组装。关于实验观察到的胶体颗粒在电极附近的依赖于电解液的运动背后的机制的假说将得到检验。实验观察到，在交流极化过程中，相位角与两个粒子的聚集或分离之间存在关联。预期角度为90度。观察到的角度对氢氧化钾小于90度，对重碳酸盐溶液大于90度。颗粒在氢氧化钾中分离，在氢氧化钾中聚集。对于电解液和电极的几种组合，已经证实了相对于90o的相位角与颗粒是聚集还是分离之间的关系。这种依赖于溶液的相关性的原因尚不清楚。假设所需的附加力来自一种被称为“法拉耦合电渗透”(FCEO)的流动机制，该流动机制由横向电场分量与电极双层中的电荷相互作用驱动。FCeO打破了电场和粒子电荷之间的“基于粒子的电渗透”(PBEO)相互作用产生的强力的对称性。FCEO改变了粒子的行为，使粒子高度和电场不呈现预期的_/2相关系。这项研究将提高对在表面形成有序颗粒层的重要作用力的认识。潜在的应用领域是传感器和光学技术。这一提议的智力价值在于，假设电场与粒子和电极的双层相互作用产生的电渗流不仅是理解极化电极附近单个粒子行为的关键，也是理解多粒子系统的聚集/分离行为的关键。证明这一假设将完成对粒子远程组装的理解。这个问题涉及到丰富的科学和工程问题；它涉及胶体、电化学和流体动力学现象的组合。拟议的研究包括新颖的实验和多物理电流体计算机模拟。拟议中的调查是完成这一最微妙效应之谜所必需的顶峰研究。更广泛的影响本研究的现象对胶体科学和技术具有根本的意义。新的显示技术利用了电场与包裹在液体中的颗粒的相互作用。电池，只要有它们的电荷，就可以通过电流体流进行操纵，甚至可以进行分类。电渗流在这个问题的细节之外的技术中很重要，特别是在液体的微流控运输中。所获得的新观点也将支持已经纳入胶体科学课程的实验室实验的发展。这项研究将是卡内基梅隆大学一名研究生和本科生培训的一部分，他们将成为科学和工程界的生产性代理人。

National Science Foundation - Division of Chemical &Transport Systems Particulate & Multiphase Processes Program (1415)Proposal Number: 0730391 Principal Investigators: Sides, Paul Affiliation: Carnegie Mellon University Proposal Title: Investigation of the Zeta Potential of Electrically PolarizedInrterfaces The field of this research is electrochemically directed self-assembly of colloidal particles on electrodes. A hypothesis about the mechanism behind an experimentally observed electrolyte-dependent motion of colloidal particles near an electrode will be tested. The experimental observation is that a correlation between a phase angle and the aggregation or separation of two particles during ac polarization exists. The expected angle is 90o. The observed angles are less than 90o for KOH and greater than 90o for bicarbonate solution. The particles separate in KOH and aggregate in KOH. This correlation between the phase angle relative to 90o and whether the particles aggregate or separate has been verified for several combinations of electrolyte and electrode. The reason for this solution dependent correlation remains unknown. The hypothesis is that the required extra force arises from a flow mechanism called "faradaically coupled electroosmosis" (FCEO) driven by interaction of lateral electric field components with charge in the electrode's double layer. FCEO breaks the symmetry of the strong force arising from the "particle based electroosmosis" (PBEO) interaction between the electric field and particles' charge. FCEO modifies the particle behavior such that the particle height and electric field do not exhibit the expected _/2 phase relationship. The research will improve knowledge of forces important in the formation of ordered layers of particles on surfaces. The potential application areas are sensors and optical technology. Intellectual Merit The intellectual thrust of this proposal is the hypothesis that electroosmotic flow due to interaction between electric fields and the double layers of the particle and electrode is the key to understanding not only the behavior of a single particle near a polarized electrode but also to understanding the aggregative/separative behavior of multi-particle systems. Proving this hypothesis would complete the understanding of remote assembly of particles. The problem is rich in science and engineering; it involves the combination of colloidal, electrochemical, and hydrodynamic phenomena. The proposed investigation includes novel experimentation and multiphysical electrohydrodynamic computer simulations. The propose investigation is the capstone study necessary to complete the puzzle of this most subtle effect. Broader Impact The phenomena of this study are of fundamental interest to colloid science and technology. New display technologies employ the interaction of electric fields with particles encapsulated with liquids. Cells, given their charge, can be manipulated by electrohydrodynamic flows and even sorted. Electroosmotic flow is important in technologies beyond the details of this problem, particularly in microfluidic transport of liquids. The new perspectives gained will also support the development of laboratory experiments already inserted into the colloid science curriculum. The research will be a part of the training of a graduate student and undergraduates at Carnegie Mellon, who will become productive agents in the scientific and engineering community.