The Composition and Chemistry at the Liquid/Vapor Interface

by John Hemminger (UC Irvine, Ca)

Friday 18 Apr 2008, 13:15 → 14:00 Europe/Stockholm

Seminar room Roslagstullsbacken 17, AlbaNova

We utilize a combination of ambient pressure x-ray photoelectron spectroscopy experiments and classical molecular dynamics simulations to study the liquid/vapor interface of aqueous solutions.
The subject will be introduced by demonstrating that the spatial distributions of ions at the aqueous solutions of alkali halides differs substantially from that of the bulk solution. In particular, our experiments show that the larger, more polarizable anions such as iodide and bromide are significantly enhanced at the interface and that a dynamic double layer is formed at the interface in which, on average, the cations are further from the surface than the anions.
We have also studied how these effects are modified by an organic surfactant layer at the interface. Finally, acid base equilibria at the surface will be described through our studies of aqueous solutions of hexylamine. We observe that the unprotonated form of hexylamine is more surface active whereas the protonated form can move into the bulk. This difference in surface activity of the unprotonated and protonated forms of hexylamine shift the surface acid/base equilibria towards more basic pH.
The implications of our results to reactions on aerosol droplets in the troposphere will be discussed.