IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Tuesday Sessions
       Session SS2-TuM

Paper SS2-TuM5
Using Nanoscale Amorphous Films to Study Mixing, Transport and Phase Separation in Deeply Supercooled, Metastable Binary Solutions of Methanol, Ethanol, and Water

Tuesday, October 30, 2001, 9:40 am, Room 122

Session: Water at Surfaces
Presenter: P. Ayotte, Pacific Northwest National Laboratory
Authors: P. Ayotte, Pacific Northwest National Laboratory
Z. Dohnalek, Pacific Northwest National Laboratory
G.A. Kimmel, Pacific Northwest National Laboratory
R.S. Smith, Pacific Northwest National Laboratory
B.D. Kay, Pacific Northwest National Laboratory
Correspondent: Click to Email
The relatively large diffusivities exhibited by amorphous deposits of water, methanol, and ethanol at cryogenic temperature (<160K) opens up the possibility to investigate liquid-phase kinetics in the deeply-supercooled, metastable thin film regime. Compositonally tailored, multilayer films grown by molecular beam dosing techniques are particularly well suited for the characterization of diffusion and desorption kinetics as shown previously for thin film water. While it is well-known that liquid mixtures of alcohol and water exhibit non-ideal solution behavior due to hydrophobic solvation, the complexity of their liquid-solid phase diagrams has been interpreted in terms of formation and decomposition of different crystalline hydrates (stochiometric and/or clathrates). We use molecular beam scattering and programmed desorption (both TPD and isothermal) to study the desorption and mixing kinetics as well as the crystallization of mixed multilayer ices of water, ethanol, and methanol. The desorption spectra exhibit complex features that depend strongly on both the film's composition and thickness. Analysis of the desorption spectra using a kinetic model that describes liquid solution evaporation reveals both the extent of mixing and the details of the solvation kinetics in the metastable liquids. We compare these results with existing liquid-solid phase diagrams for these binary mixtures. While thin binary films of methanol and ethanol exhibit ideal behavior, binary mixtures of water and either alcohol display strongly non-ideal behavior presumably caused by precipitation of solid crystalline hydrates from the deeply-supercooled, metastable liquid solutions. @FootnoteText@ P. Ayotte is an NSERC Postdoctoral Fellow. Pacific Northwest Laboratory is a multiprogram National Laboratory operated for the U. S. Department of Energy by Battelle Memorial Institute under contract DE-AC06-76RLO 1830.