10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Exploring Chemistry in Microdroplets in a Branched Quadrupole Trap
MICHAEL JACOBS, James F. Davies, Ryan Davis, Lance Lee, Frances Houle, Kevin Wilson, Lawrence Berkeley National Laboratory
Abstract Number: 506 Working Group: Aerosol Chemistry
Abstract Reactions in compartmentalized spaces are ubiquitous in nature, occurring in cells, mineral pores and aerosol droplets in the atmosphere. Recent studies have probed chemical reactions in a variety of different compartmentalized spaces, such as in an electrospray source, oil water emulsion, and thin films. These studies suggest that reactions in micron-sized compartments can occur at rates that are enhanced by several orders of magnitude compared to similar reactions in bulk solution. The experimental rate enhancements have been attributed to several different sources: increased concentration of reactants due to solvent evaporation, extreme pH in compartments due to large amounts of charge on the droplets, and interfacial effects due to the large surface to volume ratio of the compartments. While each of these explanations may play a role, a general explanation and the relative importance of each remains unclear. Ultimately, the source and generality of the observed rate enhancements has potentially far reaching implications for condensed phase aerosol chemistry as well as origin of life chemistry.
Here, I report work that has been performed using a recently developed single particle levitator (a branched quadrupole electrodynamic trap)1 to study reactions occurring in micron-sized droplets. Using this trap, two 20-50 µm droplets with different compositions are contactlessly manipulated and merged to initiate a chemical reaction. Both the composition and size of the merged droplet are controlled precisely in the trap, and the evolving reactions within the droplets are probed spectroscopically (Raman) or with single particle mass spectrometry. From these measurements, the role of the air-water interface is isolated from concentration and pH effects, and its relative importance in enhancing reaction rates is determined.
(1) Jacobs, M. I.; Davies, J. F.; Lee, L.; Davis, R. D.; Houle, F. A.; Wilson, K. R. Anal. Chem. 2017, 89 (22), 12511–12519.