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Transport in amorphous solid water films: implications for self-diffusivity. | LitMetric

Transport in amorphous solid water films: implications for self-diffusivity.

J Phys Chem B

Institute for Theoretical Chemistry and Texas Materials Institute, Department of Chemical Engineering, University of Texas at Austin, Texas 78712-0321, USA.

Published: September 2006

AI Article Synopsis

  • Thermal desorption spectroscopy is used to analyze how labeled amorphous solid water (ASW) and organic spacer layers interact and transport prior to the crystallization of ASW at low temperatures (around 150-160 K).
  • The study investigates the influence of the thickness of both ASW and the organic spacer layers on self-transport and evaluates how effective these spacers are as diffusion barriers.
  • Results reveal that instead of diffusion through a dense phase, intermolecular mixing near the crystallization temperature happens through vapor-phase transport due to cracks in the ASW film, suggesting a significant reduction in self-diffusivity before crystallization and indicating a transition in water properties above 160 K.

Article Abstract

Thermal desorption spectroscopy is employed to examine transport mechanisms in structured, nanoscale films consisting of labeled amorphous solid water (ASW, H(2)(18)O, H(2)(16)O) and organic spacer layers (CCl(4), CHCl(3)) prior to ASW crystallization (T approximately 150-160 K). Self-transport is studied as a function of both the ASW layer and the organic spacer layer film thickness, and the effectiveness of these spacer layers as a bulk diffusion "barrier" is also investigated. Isothermal desorption measurements of structured films are combined with gas uptake measurements (CClF(2)H) to investigate water self-transport and changes in ASW film morphology during crystallization and annealing. CCl(4) desorption is employed as a means to investigate the effects of ASW film thickness and heating schedule on vapor-phase transport. Combined, these results demonstrate that the interlayer mixing observed near T approximately 150-160 K is inconsistent with a mechanism involving diffusion through a dense phase; rather, we propose that intermixing occurs via vapor-phase transport through an interconnected network of cracks/fractures created within the ASW film during crystallization. Consequently, the self-diffusivity of ASW prior to crystallization (T approximately 150-160 K) is significantly smaller than that expected for a "fragile" liquid, indicating that water undergoes either a glass transition or a fragile-to-strong transition at a temperature above 160 K.

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Source
http://dx.doi.org/10.1021/jp063259yDOI Listing

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