College Park, Maryland      June 6 - 10 , 2004

T1-A1 (8:30 AM): Probing the Structure of Nanoscale Aerosols (Invited)

Barbara Wyslouzil (Department of Chemical Engineering, Ohio State University), Gerald Wilemsk (University of Missouri – Rolla), Reinhard Strey (Universität zu Köln, Germany)

Multicomponent nanometer sized droplets form readily in the supersonic expansion that occur, for example, in volcanic eruptions, jet exhausts and turbomachinery. From a fundamental point of view, particles with radii < 10 nm are important because they lie in the critical transition zone between large molecular clusters and bulk materials. The properties of the aerosol size distribution, i.e. the number density, the average particle size, and the polydispersity together determine the surface area of the aerosol. Differences between the surface and interior compositions, on the other hand affect the heterogeneous chemistry as well as the growth and evaporation kinetics. Unlike solid particles, that can be captured and subjected to further analysis, liquid droplets must be examined in situ.

Over the past 7 years, we have pioneered the use of small-angle neutron scattering (SANS) to study the properties of nanodroplet aerosols. With condensed phase volume fractions on the order of 10-6, aerosol-SANS experiments are technically challenging. The results from our experiments to date are, however, yielding important insights into particle formation processes and into the internal structure of the droplets themselves. This talk will focus on our efforts to use SANS to find direct evidence for and characterize surface enrichment in nanodroplets

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