| AVS 54th International Symposium | |
| Surface Science | Thursday Sessions |
| Session SS-ThP |
| Session: | Surface Science Poster Session |
| Presenter: | T.M. McIntire, University of California, Irvine |
| Authors: | T.M. McIntire, University of California, Irvine A.S. Lea, Pacific Northwest National Laboratory P.L. Gassman, Pacific Northwest National Laboratory Q. Li, KLA-Tencor Corporation O.S. Ryder, University of California, Irvine B.J. Finlayson-Pitts, University of California, Irvine |
| Correspondent: | Click to Email |
Airborne particles have well-documented effects on human health, visibility and the chemistry of the atmosphere. A major area of concern, but also largely uncertain, is the impact of particles on global climate. A significant part of this uncertainty is the lack of understanding of the nature of the organic component. This deficiency includes the chemical speciation and the distribution of the organics between the surface and the bulk of liquid particles, as well as changes due to oxidation during transport in the atmosphere. In this work, the formation of large organic aggregates has been observed from the ozone oxidation of unsaturated alkene self-assembled monolayers (SAMs) on solid silica surfaces. Ozonolysis of terminal alkene SAMs of 3- and 8-carbon lengths, as proxies for organic-coated airborne dust particles, leads to the formation of large hydrophobic aggregates which do not increase the uptake of water as previously assumed. These SAMs were generated on silicon substrates and reacted at room temperature with gaseous ozone. A combination of experimental techniques, atomic force microscopy, scanning electron microscopy, Auger microprobe, time-of-flight secondary ion mass spectrometry, and transmission FTIR, were used to study the surface composition and morphology after oxidation. Large (micron-size) organic aggregates formed on the surface while the surrounding substrate became depleted of carbon and exposed the original substrate. This highly unusual result establishes that the mechanism of ozonolysis of alkene SAMs involves polymerization, likely induced by secondary reactions of the Criegee intermediate (CI). For that reason, formation of polymers under atmospheric conditions may be more common than previously recognized. The uptake of water was not increased upon oxidation of these films, in contrast to current expectations. Implications for SAM reactions and stability in air, ozonolysis of alkenes on surfaces, and for the oxidation of alkenes on airborne dust particles are discussed.