Methods for Determining Length, Surface Area and Fractal Dimension of Non-spherical Particles
About the Presenter:
Professor David Y. H. Pui is Director of the Particle Technology Laboratory and of the Center Filtration Research at the University of Minnesota. He has a broad range of research experience in aerosol science and technology and has over 250 journal papers and 25 patents. He has developed several widely used commercial aerosol instruments. Dr. Pui has received many awards, including the Smoluchowski Award by the Gesellschaft fuer Aerosolforschung (1992), the Max Planck Research Award (1993), the Humboldt Research Award for Senior U.S. Scientists (2000), the David Sinclair Award by the American Association for Aerosol Research (2002), and the Fuchs Memorial Award (2010) — the highest disciplinary award conferred by the American, German and Japanese aerosol associations.
Instruments for measuring airborne particle size distributions are well established. Commercial aerosol instruments are available to measure size distributions from 2.5 to 1,000 nm with high resolution and wide concentration range. Most of these instruments deliver only equivalent particle size, e.g., mobility equivalent diameter or aerodynamic diameter of spherical particles. However, most of the real-life particles, such as Diesel soot and engineered nanoparticles, are non-spherical agglomerates. Information of agglomerates length, surface area and fractal dimension are important for toxicity assessment, for emission control of Diesel soot, and for quality control of engineered nanoparticles production.
We have developed methods for measuring length, surface area and fractal dimension of non-spherical particles. By combining a DMA (differential mobility analyzer) with a filter with uniform pores, namely a filter pre-separator, a new method for differentiating nanoparticles with different mass-mobility fractal
dimensions was developed and validated experimentally and theoretically. It can also measure the effective length (or maximum projected length) of nanoparticles with irregular shapes. Another method involves incorporating a custom-built electrostatic precipitator in the existing NSAM (Nanoparticle Surface Area Monitor for lung deposited surface area). By varying voltages on the ESP to precipitate the charge particles and by dividing the classification in two regimes, a geometrical surface area monitor is developed and validated. Details of these developments, together with instrument calibration issues, will be discussed at the Workshop.