Transport in Amorphous Solid Water Films: Implications for Self-Diffusivity
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- 作者：Sean M. McClure ; Evan T. Barlow ; Minta C. Akin ; Douglas J. Safarik ; Thomas M. Truskett ; C. Buddie Mullins
- 刊名：Journal of Physical Chemistry B
- 出版年：2006
- 出版时间：September 14, 2006
- 年：2006
- 卷：110
- 期：36
- 页码：17987 - 17997
- 全文大小：2498K
- 年卷期：v.110,no.36(September 14, 2006)
- ISSN：1520-5207
文摘
Thermal desorption spectroscopy is employed to examine transport mechanisms in structured, nanoscale filmsconsisting of labeled amorphous solid water (ASW, H218O, H216O) and organic spacer layers (CCl4, CHCl3)prior to ASW crystallization (T 
150-160 K). Self-transport is studied as a function of both the ASW layerand 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 gasuptake measurements (CClF2H) to investigate water self-transport and changes in ASW film morphologyduring crystallization and annealing. CCl4 desorption is employed as a means to investigate the effects ofASW film thickness and heating schedule on vapor-phase transport. Combined, these results demonstratethat the interlayer mixing observed near T 150-160 K is inconsistent with a mechanism involving diffusionthrough a dense phase; rather, we propose that intermixing occurs via vapor-phase transport through aninterconnected network of cracks/fractures created within the ASW film during crystallization. Consequently,the self-diffusivity of ASW prior to crystallization (T 150-160 K) is significantly smaller than that expectedfor a "fragile" liquid, indicating that water undergoes either a glass transition or a fragile-to-strong transitionat a temperature above 160 K.
150-160 K). Self-transport is studied as a function of both the ASW layerand 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 gasuptake measurements (CClF2H) to investigate water self-transport and changes in ASW film morphologyduring crystallization and annealing. CCl4 desorption is employed as a means to investigate the effects ofASW film thickness and heating schedule on vapor-phase transport. Combined, these results demonstratethat the interlayer mixing observed near T 150-160 K is inconsistent with a mechanism involving diffusionthrough a dense phase; rather, we propose that intermixing occurs via vapor-phase transport through aninterconnected network of cracks/fractures created within the ASW film during crystallization. Consequently,the self-diffusivity of ASW prior to crystallization (T 150-160 K) is significantly smaller than that expectedfor a "fragile" liquid, indicating that water undergoes either a glass transition or a fragile-to-strong transitionat a temperature above 160 K.