Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session W42: Focus Session: Supercooled and Nanoconfined Water IV |
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Sponsoring Units: DCP Chair: Valeria Molinero, University of Utah Room: Hilton Baltimore Holiday Ballroom 3 |
Thursday, March 21, 2013 2:30PM - 3:06PM |
W42.00001: Freezing of supercooled water nanodroplets Invited Speaker: Barbara Wyslouzil All three states of water play important roles in nature, from thermostating the atmosphere to providing reactive surfaces environments. The rates at which transitions between the phases occur, the degree to which pure liquid water can be supercooled, and the solid phases that form are all fundamentally interesting questions with strong atmospheric relevance. We have followed and characterized the nucleation, growth, and subsequent freezing of pure water droplets formed in a supersonic nozzle apparatus using both Small Angle X-ray Scattering (SAXS) and Fourier Transform Infrared Spectroscopy (FTIR). Because the droplets have radii $r$ between 3 nm and 6 nm, and the cooling rates are on the order of 5E5 K/s, liquid water only begins to freeze below approximately 215 K. These temperatures are well below the homogeneous freezing limit for bulk water. The experiments show the expected decrease in freezing temperature with decreasing droplet size, or alternatively, with increasing droplet internal pressure. [Preview Abstract] |
Thursday, March 21, 2013 3:06PM - 3:42PM |
W42.00002: Probing no man's land: ice nucleation at the nanoscale Invited Speaker: Tianshu Li Nucleation is a stochastic process. At a given thermodynamic condition, nucleation events occur at a frequency that scales with the volume of the system. Therefore at the nanoscale, {\em e.g.}, in nano droplets, one may expect to obtain supercooled liquids below the bulk homogeneous nucleation temperature. However it is not clear to what extent would nucleation in nano droplet be connected with bulk water. In this talk, I will discuss the insight gained from our recent molecular simulations on ice nucleation at nanoscale. In particular, the study provides direct computational evidence for size-dependent ice nucleation rate within supercooled water nano droplets. Using a thermodynamic model based on classical nucleation theory, I will show that it is the Laplace pressure induced by the curved liquid vapor interface present in droplets that is responsible for the suppression of ice crystallization. Consistent with this model, our simulations show that the nucleation rates found for droplets are similar to those of liquid water subject to a pressure of the order of the Laplace pressure within droplets. The findings thus provide a link between supercooled bulk water and nano droplet through ice nucleation rate. In addition, the findings also support the hypothesis of surface crystallization of ice in microscopic water droplets in clouds. [Preview Abstract] |
Thursday, March 21, 2013 3:42PM - 3:54PM |
W42.00003: Experimental Observation of Bulk Liquid Water Structure in ``No Man's Land'' Jonas Sellberg, Trevor McQueen, Congcong Huang, Duane Loh, Hartawan Laksmono, Raymond Sierra, Christina Hampton, Dmitri Starodub, Daniel DePonte, Andrew Martin, Anton Barty, Thor Wikfeldt, Daniel Schlesinger, Lars Pettersson, Martin Beye, Dennis Nordlund, Thomas Weiss, Jan Feldkamp, Chiara Caronna, Marvin Seibert, Marc Messerschmidt, Garth Williams, Sebastien Boutet, Michael Bogan, Anders Nilsson Experiments on pure bulk water below about 235 K have so far been difficult: water crystallization occurs very rapidly below the homogeneous nucleation temperature of 232 K and above 160 K, leading to a ``no man's land'' devoid of experimental results regarding the structure. Here, we demonstrate a new, general experimental approach to study the structure of liquid states at supercooled conditions below their limit of homogeneous nucleation. We use femtosecond x-ray pulses generated by the LCLS x-ray laser to probe evaporatively cooled droplets of supercooled bulk water and find experimental evidence for the existence of metastable bulk liquid water down to temperatures of 223 K in the previously largely unexplored ``no man's land''. [Preview Abstract] |
Thursday, March 21, 2013 3:54PM - 4:06PM |
W42.00004: Glass softening, crystallization, and vaporization of nano-aggregates of Amorphous Solid Water: Fast Scanning Calorimetry studies Deepanjan Bhattacharya, Liam O'Reilly, Vlad Sadtchenko Despite intense efforts, complete understanding of relationships between various condensed phases of water remains an elusive goal. In particular, the molecular kinetics and phase transitions of water in confining geometries (e.g., nano-scale films) are of special interest due to the relevance to environmental and biological processes. With the objective of gaining insights into fundamental distinctions in physical and chemical properties of confined water, we have developed an experimental approach which relies on rapid (10$^5$~K/s) heating of nanoscale films of Amorphous Solid Water (ASW) prepared by vapor deposition in vacuum at cryogenic temperatures. With recent advances, the approach, Fast Scanning Calorimetry (FSC), facilitates studies of glass softening, crystallization, and vaporization of ASW films with thicknesses down to two nanometers. Unlike bulk samples, the thermograms of ultrathin ASW films show two endotherms at 40 and 10 K below the onset temperatures of crystallization. We will report the conclusion of our analysis of the FSC thermograms of nanoscale ASW aggregates, and discuss the implications of these studies for developing better models of molecular kinetics of water in confining geometries. [Preview Abstract] |
Thursday, March 21, 2013 4:06PM - 4:18PM |
W42.00005: Temperature dependence of the Oxygen-Oxygen separations in water from high energy x-ray diffraction Lawrie Skinner, Chris Benmore, John Parise We have used state of the art, high energy x-ray diffraction to obtain detailed measurements of the Oxygen-Oxygen (O-O) pair distribution function (g(r)) of liquid water between -20 and 92 degrees Celsius. These measurements show ordinary linear behavior of the first O-O distance, over the full temperature range, even through the density maximum. Conversely we do see interesting, non-linear behavior in the O-O distribution at higher separations distances, particularly around the 4.5{\AA} peak. Another interesting feature of these measurements is the presence of a temperature-independent crossover point in the running O-O coordination number at the location of the first minimum in r$^{2}$[g(r)-1], which defines the end of the first shell. At this 3.4(1){\AA} distance the O-O coordination number is 4.5(2) at all the temperatures studied. We believe this work offers important insight into some of the unusual physical properties of water, and provides a valuable validation point for the many Molecular dynamics models of liquid water. [Preview Abstract] |
Thursday, March 21, 2013 4:18PM - 4:54PM |
W42.00006: The structure of ice crystallized from supercooled water Invited Speaker: Benjamin Murray The freezing of water to ice is fundamentally important to fields as diverse as cloud formation to cryopreservation. Traditionally ice was thought to exist in two well-crystalline forms: stable hexagonal ice and metastable cubic ice. It has recently been shown, using X-ray diffraction data, that ice which crystallizes homogeneously and heterogeneously from supercooled water is neither of these phases. The resulting ice is disordered in one dimension and therefore possesses neither cubic nor hexagonal symmetry and is instead composed of randomly stacked layers of cubic and hexagonal sequences. We refer to this ice as stacking-disordered ice I (ice I$_{sd})$. This result is consistent with a number of computational studies of the crystallization of water. Review of the literature reveals that almost all ice that has been identified as cubic ice in previous diffraction studies and generated in a variety of ways was most likely stacking-disordered ice I with varying degrees of stacking disorder, which raises the question of whether cubic ice exists. New data will be presented which shows significant stacking disorder (or stacking faults on the order of 1 in every 100 layers of ice I$_{h})$ in droplets which froze heterogeneously as warm as 257 K. The identification of stacking-disordered ice from heterogeneous ice nucleation supports the hypothesis that the structure of ice that initially crystallises from supercooled water is stacking-disordered ice I, independent of nucleation mechanism, but this ice can relax to the stable hexagonal phase subject to the kinetics of recrystallization. The formation and persistence of stacking disordered ice in the Earth's atmosphere will also be discussed. [Preview Abstract] |
Thursday, March 21, 2013 4:54PM - 5:06PM |
W42.00007: Investigation of water-graphite interaction using molecular beam technique. Nobuya Miyoshi, Shohei Hodota, Kenichi Osuka, Ikuya Kinefuchi, Shu Takagi, Yoichiro Matsumoto We have investigated water scattering from a graphite surface using the molecular beam technique. The time-of-flight and angular distributions of the scattered molecules were measured at the incident energy lower than 100 meV with the surface temperature of 300 K. As the incident energy decreases from 35 to 130 meV, adsorption-desorption component increases in the time-of-flight distributions. At the incident energy of 35 meV, the angular flux distribution deviates from lobular pattern and approaches to cosine distribution. The final energy of the scattered molecules at the incident energy of 35 meV becomes less dependent on the scattering angle than at the incident energy of 130 meV. These results confirm that the reduction of the incident energy from 130 to 35 meV enhances the accommodation of water molecule to graphite surface. [Preview Abstract] |
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