Interaction of SAMs with Oxidants and Water
Current research focuses on self-assembled monolayers (SAMs), their
interactions with water, and their oxidation in the presence and absence of thin
water films. For example:
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SAMS on solid substrates and their oxidation by atmospheric oxidants such as ozone
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Water uptake on SAMs comprised of single or multi-component mixtures
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Oxidation of mixed SAMs in the presence of water
One approach in the Finlayson-Pitts group is the use of ATR-FTIR for studying SAMs and their interaction with water and atmospheric oxidants.
Schematic of ATR-FTIR system for real-time studies of SAM oxidation
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MD simulations by the Tobias group provide insight into the interaction of gases with SAMs. For example, they predict that ozone undergoes multiple encounters with the surface during a "collision" due to van der Waals attractions, rather than simply undergoing an elastic collision. This results in an enhancement in the collision rate between ozone and reactive sites on the SAM surface relative to the theoretical prediction. These results are compared to simulations of ozone interacting with other proxies for organic aerosols. The proxies being studied include organic liquids (1-tetradecene, oleic acid) and organic monolayers adsorbed on water (phospholipids, oleic acid). In general, the MD simulations are used to identify the important molecular factors in the oxidative processing of organic aerosols. Simulations of the interaction of water with SAMs is being carried out by Martina Roeselová at the Academy of Sciences of the Czech Republic. These will interface closely with the experiments carried out in the Finlayson-Pitts, Hemminger, and Nizkorodov groups. A variety of surface science approaches are used by the Hemminger group to study the interaction of SAMs with water and with oxidants. The techniques used include thermal or laser desorption from alkylthiol SAMs on a gold surface, with monitoring of the desorbing species or reaction products by mass spectrometry. For example, in the thermal desorption chamber shown below, controlled rapid heating of the sample is coupled with monitoring by mass spectrometry of the species that desorb as the sample is heated. The sample can be positioned either in front of the mass spectrometer or in front of the doser.
Photo of laser desorption mass spectrometry chamber This chamber is being used in the Hemminger group to study the interaction of SAMs with water and other gaseous species. Of particular interest is whether uptake of gases will be enhanced in the pores of corrugated surfaces formed by a mixture of SAMs as illustrated below.
Schematic of possible uptake of gases by mixed SAMs |
