GOALI: Unipolar Diffusion Charging of Spherical and Agglomerated Nanoparticles and its Application toward Surface-area Measurement

纳米粒子的许多重要特性与它们极高的表面体积比有关，包括催化活性、生物利用度、健康效应和在环境中的反应性。本项目研究纳米粒子及其团聚体/聚集体的基本单极电荷机制。通过将单极电荷和静电沉积相结合来开发一种仪器，它将能够在线测量具有各种形态的空气中纳米颗粒的几何表面积。到目前为止，只能测量所谓的Fuchs或BET表面积，这并不能提供有关空气中粒子的几何表面积的信息。本研究将进行扩散充电机制的基础研究。所研究的颗粒尺寸将从几百纳米到20纳米以下的球形，以及80纳米以下的团聚体和聚集体。松散团聚体和部分烧结团聚体之间的充电速率将通过实验和理论确定。仪器开发工作将在UMN和TSI实验室进行，其中包括：(1)离线测定团聚体和团聚体的表面积，(2)研究电荷和静电沉积相结合的颗粒表面积测量，其中将包括我们的德国合作者开发的静电除尘器（ESP），以及(3)充电器，离子阱和ESP对团聚体和团聚体的整体响应。团聚体的电荷分布和静电沉积效率与球体不同。我们的研究将阐明电荷和静电沉积对粒子形态的主要依赖关系。知识价值和更广泛的影响：这项提出的研究将促进对粒子形态对纳米粒子单极电荷和静电沉积的影响的理解。这将有助于开发一种在线测量球形和凝聚纳米颗粒总几何表面积的方法。这种方法可以有广泛的应用，因为在纳米颗粒制造的过程控制、纳米颗粒毒性研究的剂量测定、暴露测量和许多其他应用中需要快速和在线的纳米颗粒表面积测量。这将在研究工程纳米颗粒的环境、健康和安全（Nano-EHS）意义上发挥重要作用。纳米- ehs问题将成为社会的突出问题，也是刚刚发布的NRC关于工程纳米材料的环境、健康和安全方面的研究战略报告（2012）的主题。David Pui是两个欧盟纳米- ehs项目的顾问委员会成员：SCAFFOLD和NANODEVICE。去年，他担任第五届纳米技术、职业和环境健康国际研讨会的顾问委员会成员，并担任毒理学学会年会“职业环境中纳米颗粒暴露评估圆桌讨论”的小组成员。在过去的两年中，他在各种国际研讨会上就纳米ehs主题做了七次全体演讲。这项研究项目取得的成果将通过这些外联渠道传播。我们还计划将这些知识融入到我们的教学活动中。例如，David Pui参与了一门关于纳米技术与社会的公共事务、法律和生物伦理学联合课程的教学（明尼苏达大学PA 8790/ law 6037/BTHX 8000课程）。

CBET-1236107Many important properties of nanoparticles are related to their extremely high surface to volume ratios, including catalytic activity, bioavailability, health effects, and reactivity in the environment. This project studies the fundamental unipolar charging mechanics of nanoparticles and their agglomerates/aggregates. By combining unipolar charging and electrostatic deposition to develop an instrument, it will enable online measurement of the geometric surface area of airborne nanoparticles with various morphologies. Thus far it is only possible to measure the so-called Fuchs or BET surface area, which do not provide information about the geometric surface area of airborne particles.The research will perform fundamental studies on diffusion charging mechanisms. Investigated particle sizes will be from several hundred nanometers down to below 20 nm for spheres, and below 80 nm for agglomerates and aggregates. Charging rates between the loose agglomerates and partially sintered aggregates will be determined experimentally and theoretically. Instrument developmental effort will be performed at both UMN and TSI laboratories, which will involve: (1) offline determination of the surface area of the agglomerates and aggregates, (2) investigation of the combination of charging and electrostatic deposition for the measurement of particle surface area, which will incorporate the Electrostatic Precipitator (ESP) developed by our German collaborators, and (3) overall response of the charger, ion trap and ESP for agglomerates and aggregates. The charge distributions and electrostatic deposition efficiencies of agglomerates are different from those of spheres. Our study will elucidate principal dependencies of charging and electrostatic deposition on particle morphology.Intellectual Merit and Broader Impacts:This proposed study will advance understanding of the effects of particle morphology on unipolar charging and electrostatic deposition of nanoparticles. This will help to develop a method for online measurements of total geometric surface area of spherical and agglomerated nanoparticles. Such a method can have a wide range of applications since fast and online nanoparticle surface area measurement is desirable in process control of nanoparticle manufacturing, in dosage determination for nanoparticle toxicity studies, in exposure measurement and many other applications. It will play an important role in studying environmental, health and safety (Nano-EHS) implications of engineered nanoparticles. The Nano-EHS issues will be prominent in society and is the theme of the just released NRC Report on Research Strategy for Environmental, Health, and Safety Aspects of Engineered Nanomaterials (2012). David Pui serves on the Advisory Board of two EU Nano-EHS programs: SCAFFOLD and NANODEVICE. Last year, he served on the Advisory Board of the 5th International Symposium on Nanotechnology, Occupational and Environmental Health, and was a panelist of the Roundtable Discussion on Assessment of Nanoparticle Exposure in Occupational Settings at the Society of Toxicology Annual Meeting. During the past two years, he presented seven plenary lectures at various international symposia on the Nano-EHS topic. Results obtained from this research project will be disseminated through these outreach channels. We also plan to integrate the knowledge into our teaching activities. For example, David Pui is involved in the teaching of a joint public affairs, law and bioethics course on Nanotechnology and Society (PA 8790/Law 6037/BTHX 8000 course at the University of Minnesota).