Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session A34: Environmental Interfaces I |
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Sponsoring Units: DCP Chair: Franz Geiger, Northwestern University Room: LACC 511A |
Monday, March 21, 2005 8:00AM - 8:36AM |
A34.00001: Creating Beakers without Walls: Formation of Deeply-Supercooled Binary Liquid Solutions from Nanoscale Amorphous Solid Films Invited Speaker: Supercooled liquids are metastable and their lifetimes are dictated by the kinetics for crystallization. Traditional experimental studies have used a variety of methods to suppress crystallization while cooling from the liquid phase. An alternate approach is to heat an amorphous solid above its glass transition temperature, Tg, whereupon it transforms into a deeply-supercooled liquid prior to crystallization. We employ molecular beams, programmed desorption (both TPD and isothermal) and FTIR vibrational spectroscopy to synthesize and characterize compositionally tailored nanoscale films of glassy methanol and ethanol. We demonstrate that these films exhibit complete diffusive intermixing and suppressed crystallization when heated above Tg. Furthermore, the resulting container-less liquids evaporate as continuously mixed ideal binary solutions while retaining their solid-like macroscopic shapes. This approach provides a new method for preparing deeply-supercooled liquid solutions in metastable regions of their phase diagram and for studying the kinetics of their phase separation and crystallization as they approach thermodynamic equilibrium. The applicability of this technique for studying aqueous liquid solutions will also be presented and discussed. [Preview Abstract] |
Monday, March 21, 2005 8:36AM - 8:48AM |
A34.00002: Growth-Melt Asymmetry in Ice A. Cahoon, M. Maruyama, J.S. Wettlaufer It is well known that the Wulff Shape of a crystal is anisotropic at temperatures below the roughening temperatures for the principal facets. In the case of ice in contact with water, the roughening temperature of the prism facet was found by Maruyama to be -16.5 deg C, whereas the basal plane is molecularly smooth up to the bulk transition. Therefore, {\it growth} of ice in this range of temperature is anisotropic. We study the anisotropy during {\it melting} under small disequilibrium melt drives and extend geometric theory to explain the apparent reorientation of the underlying crystallographic axes observed experimentally. The dynamical melt shapes appear faceted despite the lack of a surface phase transition and we explain the behavior using a geometric treatmen of the basic kinetics of molecular detachment from the surface. [Preview Abstract] |
Monday, March 21, 2005 8:48AM - 9:24AM |
A34.00003: Surface structure of liquids and salt solutions: wetting, droplets and monolayers Invited Speaker: The structure of water surfaces and films on solid substrates is one of the most important and relevant topics in interfacial science. Surprisingly, at the start of the 21$^{st}$ century we do not have yet a detailed knowledge of such basic problems as the thickness of a water film on a surface in equilibrium with vapor or humidity. Even less is known about the structure of this film and the molecular arrangement of water molecules at the surface and in the layers close to it. In this presentation I will review recent results in my laboratory regarding water films, both in ambient conditions (near atmospheric) as well as in vacuum using techniques such as AFM, STM, and Photoemission. [Preview Abstract] |
Monday, March 21, 2005 9:24AM - 9:36AM |
A34.00004: Effect of Antifreeze Glycoprotein in contact with ice interface on the growth mechanism of an ice crystal Etsuro Yokoyama, Yohsinori Furukawa We study the effect of Antifreeze Glycoprotein in contact with ice interface on pattern formation of an ice crystal growing from AFGP solution. AFGP effects on ice crystal growth are completely opposite for basal and prismatic faces. Basal face of ice in pure water is governed by slow molecular rearrangements on the basal plane and is expressed as a second power of the supercooling at the interface. In the presence of AFGP molecules on the surface, the kinetic roughening transition from a smooth surface to a rough one occurs, and the growth rate is enhanced. Prismatic faces in pure water are controlled by transport of latent heat and are proportional to the supercooling at the interface. In the presence of AFGP molecules, the kinetic smoothing transition from a rough surface to smooth one occurs, and the growth rate is reduced. The effects relate to the anisotropic adsorption properties of AFGP molecules. In this study, we proposed a new model for the ice growth kinetics, in which a change of structure of water molecules near ice interface, i.e., hydrophobic interaction is taken into account instead of Gibbs-Thomson Effect caused by the pinning of a step by AFGP molecules. [Preview Abstract] |
Monday, March 21, 2005 9:36AM - 9:48AM |
A34.00005: First Principles Simulations of Ice Nucleation at Metal Surfaces Angelos Michaelides, Matthias Scheffler Ice nucleation at solid surfaces is of relevance to countless scientific and technological processes. In particular the nucleation of ice nano-crystals on metal surfaces is often a key first step in cloud formation and corrosion [1]. Yet unfortunately this remains one of the most poorly understood natural phenomena; severely lacking in atomic level understanding. Here, we discuss detailed density functional theory studies aimed at putting our understanding of ice nucleation at metals on a much firmer footing. Specifically the properties of H$_2$O hexamers - the smallest `building blocks' of ice - adsorbed on a number of close-packed transition metal surfaces have been examined. We find that the competing influences of substrate reactivity and hexamer-substrate epitaxial mismatch conspire to yield a rich variety of (novel) hexameric ice structures, some of which have been observed by recent scanning tunnelling microscopy experiments [2]. [1] H.R. Pruppacher and J.D. Klett, \textit{Microphysics of Clouds and Precipitation}, (Kluwer, Dordrecht, 2003). [2] K. Morgenstern, \textit{et al.}, (To be published). [Preview Abstract] |
Monday, March 21, 2005 9:48AM - 10:00AM |
A34.00006: Grain Boundary Melting in Ice Erik Thomson, J.S. Wettlaufer, L.A. Wilen The central influence that grain boundary melting has on the sintering, coarsening, transport behavior and many other bulk properties in ostensibly all materials, including ice, motivates combined experimental and theoretical studies. The great difficulty of directly accessing a grain boundary in thermodynamic equilibrium has resulted in a dearth of experimental tests. Our approach is to prepare an ice bicrystal in a thin growth cell and to probe the grain boundary directly by employing light scattering and polarization with a helium-neon laser. We first measure the direction of the c-axis of each of the grains by bringing polarized light through each domain and analyzing the polarization of the transmitted beam. We then monitor the reflected intensity as a function of temperature and concentration of monovalent electrolyte. Using scattering theory, we estimate that, if the grain boundary is dry, the reflected intensity for a high angle grain boundary will be 10$^{-5}$ times the incident intensity. Using the index of refraction of bulk water to approximate the degree of sensitivity to the presence of a grain-boundary film, the change in reflected intensity due to a 15 $\AA$ layer of water is found to be greater than 10 \%, an easily measurable signal using a 4mW laser. Results are compared with a recent theory of impurity--stimulated grain boundary melting [Preview Abstract] |
Monday, March 21, 2005 10:00AM - 10:12AM |
A34.00007: Nucleation, condensation, wetting and dewetting of water on a silver surface Susan Dounce, Shih-Hui Jen, Minchul Yang, Hai-Lung Dai Water adsorption and nucleation on a single crystal silver surface has been characterized over the temperature range of 100 - 170 K. At temperatures greater than 165.5 K, Second Harmonic Generation studies show that water can not be condensed on the Ag surface even though the condensation rate is faster than the desorption rate. At this temperature classical nucleation theory predicts a very large critical nucleus size such that stable nuclei cannot form under normal laboratory deposition conditions. In the temperature range of 133.5 - 165.5 K SHG during isothermal adsorption-desorption and temperature programmed desorption experiments show that water desorbs from three-dimensional structures on the surface with a desorption energy of 48 kJ/mol. In contrast, at temperatures less than 133.5 K, water desorbs from a 2-D structure with an activation energy of 25 kJ/mol. In this lowest temperature range water wets the silver surface. This wetting-dewetting transition can be understood in terms of classical nucleation theory where below 133.5 K the critical nucleus height is less than one monolayer. [Preview Abstract] |
Monday, March 21, 2005 10:12AM - 10:24AM |
A34.00008: Surface Segregation in Mixed Alkali Halide Solutions Sutapa Ghosal, John Hemminger, Hendrik Bluhm, B. Simon Mun, Guido Ketteler, Miquel Salmeron Bromine compounds in the marine troposphere have been of great interest since the observation that tropospheric ozone depletion events in the arctic are correlated with gas phase bromine chemistry. Reactions with sea salt aerosols, particles and ice appears to be the source of these bromine compounds. In previous experiments we have shown that bromine segregates to the surface of sodium chloride crystals that are uniformly doped with low levels of bromide. We describe here experiments in which we have used high pressure photoelectron spectroscopy (HPPES) at the Advanced Light Source (ALS) to measure the ion concentrations at the surface of mixed alkali halide \textbf{solutions}. The experiments start with single crystals of sodium chloride that are uniformly doped with bromide at 7{\%} and 0.1{\%} level. The x-ray photoelectron spectra of the sample surface are obtained as a function of water vapor up to and at sample deliquescence. The concentrations of bromide and chloride ions at the liquid/vapor interface for the saturated solution that is produced upon deliquescence are obtained. For both samples, after deliquescence the bromide concentration at the surface of the saturated solution is greatly enhanced. The results will be compared with molecular dynamics simulations of a mixed bromide/chloride solution. [Preview Abstract] |
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