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

University Of Minnesota-Twin Cities, Minneapolis MN

Investigators

Abstract

CBET-1236107 Many 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).