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| - D2O Water Interaction with Mixed Alkane Thiol Monolayers of Tuned Hydrophobic andHydrophilic Character
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| - We have used temperature-programmed desorption (TPD) experiments to characterize the interaction betweenD2O water and a self-assembled monolayer (SAM) of mixed hydrophobic and hydrophilic thiols on Au(111).Two-component SAM surfaces with tuned hydrophobic and hydrophilic character have been formed byexposing gold samples to solutions of octanethiol and 6-mercaptohexanoic acid in varying millimolarconcentrations. Water desorption spectra from the pure hydrophobic surface exhibit first-order desorption atlow coverage with the onset of zero-order character at ∼1 Langmuir with narrow peaks at ∼145 K. In contrast,desorption of D2O water from the pure carboxylic acid-terminated surface exhibits broad peaks shifted tohigher temperatures. Interestingly, water TPD spectra from a 50% octanethiol/50% 6-mercaptohexanoic acidsurface closely resemble desorption from the purely hydrophobic octanethiol SAM. Increasing the surfaceacid fraction beyond 50% shifts the TPD profiles to higher temperatures with long, high-temperature tailsthat approach the behavior of water desorbing from the hydrophilic 6-mercaptohexanoic acid surface. Wediscuss the implications for water interaction with “textured” organic surfaces as well as with atmosphericallyrelevant organic aerosol particles. In particular, the results suggest that significant surface oxidation is necessaryto impact the interaction of water with organic aerosol surfaces.
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