Jim Cowin
Laboratory Fellow, Fundamental and Computational Sciences Directorate, Chemical and Material Sciences Division, Chemical Structure and DynamicsMatrixed Organization
Pacific Northwest National Laboratory, Environmental Molecular Sciences Laboratory
Current Activities and Projects
Recreating Complex Aqueous Interfaces
Complex interfaces such as those found at soil-water interfaces, at liquid-liquid boundaries, atmospheric aerosols, and in electrochemistry, have been difficult to probe, leaving much guess-work as to how reactions occur at them. We have been using single crystal substrates to grow liquid-like films of water and organics, to probe these important liquid-solid and liquid-liquid interfaces. Ices of water, hexane, or other hydrocarbons make good models for these liquids near an interface, especially when deposited in amorphous forms. We imbed in or on these ices, molecules and/or molecular ions, and then follow the thermal or photolytic chemistry. Upon heating of these composites, true fluidity occurs above the glass temperatures of the materials, permitting monitoring various kinetic processes directly. In this way we control precisely the distances over which chemical diffusion and charge transfer must occur, and provide a nearly ideal system to compare with theory.
In various studies we have probed and mapped the solvation potential at the oil-water interface. We also studied the variation of a liquid's fluidity near an interface. For 3-methylpentane (3MP), the interface is strongly perturbed for about 7 monolayers from either the 3MP-vacuum interface, or the 3MP-platinum interface. It is as much as 6 orders of magnitude less viscous near the vacuum, and almost as many times more viscous near the platinum interface. We look forward to expanding this research into new directions. Much of this work has been made posible via the following innovation:
Soft-Landing of Ions
We have built a special, very low energy ion beam (to 1/2 eV) to deposit mass-selected molecular ions like H3O+, NH4+, OH-, NO3-, as well as Cs+, on these liquid-solid interface model systems. With this unique ion source we have looked at water and organic solvent thin films interacting with ions like hydronium (H3O+, D3O+) and Cs+ . We use a Kelvin probe to monitor the ion height in the film (10 to 4000 monolayers) from 30 to 160 K. We study ion transport, crystallization, solvation, dielectric responses, etc. This new approach has already yielded many exciting surprises on fundamental properties of water and ultrathin liquids, and we are extending its application to higher temperatures and to micelles and-like membranes
Fundamental Properties of Water Ice
The hydronium and other ions of our soft landing ion source have made some really novel studies possible of both crystalline and amorphous water ice. In one case, we showed the famous Grotthus mechanism of extended proton tunnelling in crystalline ice, does not actually happen. In much better agreement with modern theory, we see no long-range tunnelling...as the proton self traps. We also have made the first measurements of the pyro-and piezo-electric coefficients of ice (using partially aligned water ices), and have performed other studies of partially aligned water ice. We just wrote a paper applying this knowledge to helping understand how icy grains in pre-solar nebulae might agglomerate fast enough to form planets, before the stellar wind disperses the nebulae.
Atmospheric Aerosol Surface Reactions
The role of aerosol reactions has strong impacts on the chemistry of the atmosphere, from stratospheric reactions on ice clouds or shuttle exhaust impacts on ozone, to urban/regional chemistry of air-pollutants. We have been studying this chemistry in both the laboratory and field environments. We have often employed single particle studies of the chemistry, using a computer-controlled, field emitter Environmental scanning electron microscope. This permits, with 2 nanometer resolution, us to measure both particle morphology and elemental composition, and at 8 nm resolution, at up to 10 torr of ambient water vapor conditions. We have looked at reactions of minerals, sea salt, and soots with ambient trace acid vapors and hydroxyl radicals, and find profound changes in composition and hydroscopicity. This work has been done in collaboration with Alex Laskin of PNNL. External users/collaborators in this work have included Mario and Luisa Molina of MIT, Barbara Finlayson-Pitts of U. Cal. Irvine, Vickie Grassian of U. Iowa, and other researchers at Columbia University, the National Park Service, Colorado State U., etc.
Research Interests
- Dynamics of interfacial processes
- charge transfer at interfaces
- fluidity of nanometer assemblies
- ionic processes at interfaces
- models of soil/atmospheric aerosol chemistry
Past Experience
- Postdoctoral Studies , University of Toronto with Professor John Polanyi, 1981-3
- Assistant Professor of Chemistry, University of California at Santa Barbara, 1983-90
Education
Dr. Cowin received his Ph.D. from the University of Chicago in 1981, working with Professor Lennard Wharton.
