|
|
|
|
|
Ronald L. Grimm |
||||||||||||||||||||||||||||||||||
Ron studies fundamental interactions between adsorbed water and self-assembled organic monolayers of varying hydrophobic and hydrophilic character. Recent advances in atmospheric chemistry demonstrate that aerosol surfaces play a very important role in their chemistry. In particular, organic aerosol is aged and processed through photochemical and radical oxidation reactions. These reactions likely affect each aerosol particle uniquely, resulting in a patchwork of molecules and chemical functionalities even on originally homogeneous aerosol. The end result of these reactions is likely a surface with mixed hydrophilic and hydrophobic character. The Hemminger group seeks to understand the interaction of water vapor with this patchwork aerosol surface on a fundamental molecular level. The degree of water interacting with a surface determines possible reaction pathways and the propensity for aerosol to act as cloud condensation nuclei (CCN). Self-assembled monolayers (SAMs) consisting of both hydrophilic and hydrophobic thiols simulate the patchwork aerosol surface. These thiols are allowed to adsorb onto gold from the gas phase which likely results in nanometer sized domains of hydrophobic and hydrophilic character. Following the formation of these monolayers, the surface is cooled and exposed to water which binds across the surface. As the sample is subsequently heated, water desorbs from the surface according to how tightly it binds to its specific location (it takes more heat to desorb from a hydrophilic region than a hydrophobic region!). We relate the desorption profile to the original surface to gain a more fundamental understanding of water's interaction with atmospheric aerosol.
This Table of Contents figure from our recent communication presents a number of relevant findings (J. Phys. Chem. C 2008 112(4), 890-894). In the case of a 50% methyl-terminated / 50% carboxylic acid-terminated thiol surface, water exhibits weak interactions. This is weak adsorption energy is indicated by a low temperature desorption peak centered at ~140K, somewhat lower than water desorption from a purely methyl-terminated surface. As the surface concentration of carboxylic acid-terminated thiols increases, water desorption shifts to higher temperatures indicating progressively stronger water-surface interactions. Only at high relative surface acid concentrations does the water desorption resemble the desorption from the completely acid-terminated surface. In particular, the results suggest that significant surface oxidation may be necessary to impact the interaction of water with organic aerosol surfaces.
D2O water interaction with mixed alkane thiol monolayers of tuned hydrophobic and hydrophilic character
Probing interfacial chemistry of single droplets with field-induced droplet ionization mass spectrometry: Physical adsorption of polycyclic aromatic hydrocarbons and ozonolysis of oleic acid and related compounds
Dynamics of field-induced droplet ionization: Time-resolved studies of distortion, jetting, and progeny formation from charged and neutral methanol droplets exposed to strong electric fields
Complexation of gas-phase metal ions with furan: Experimental and quantum chemical binding energies
Field-induced droplet ionization mass spectrometry
Hypervelocity microparticle impact studies using a novel cosmic dust mass spectrometer
Evaporation and discharge dynamics of highly charged droplets of heptane, octane, and p-xylene generated by electrospray ionization
|
|||||||||||||||||||||||||||||||||||
