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Wetting and melting in a methane/graphite system

Pettersen, M. S. and Lysek, M. J. and Goodstein, D. L. (1989) Wetting and melting in a methane/graphite system. Langmuir, 5 (3). pp. 563-566. ISSN 0743-7463. doi:10.1021/la00087a004.

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We report a new thermodynamic analysis of melting in thick adsorbed films and experimental results of an NMR survey of melting in methane films adsorbed on graphite. We find that solid-liquid stratification, related to surface melting in the bulk, may occur in a system that also exhibits triple point dewetting. Each phenomenon has distinctive asymptotic thermodynamic behavior in the thick film limit. We predict the existence of surface tension induced surface freezing, symmetric with surface melting, and new first-order phase transitions at coexistence between stratified and homogeneous films. The NMR data are used to show that solid methane wets graphite to at least 50 layers and that capillary condensation is not nucleated in our system (methane on Grafoil). We confirm that solid-liquid stratification does not occur in this system. Instead, melting is a first-order phase transition between homogeneous phases of solid and liquid, which we trace from a triple point dewetting transition at bulk coexistence down to 1.8 layers, where the latent heat of melting is known to have vanished. We conclude that melting in this system has a tricritical point at about 4 layers. Finally, we observe an increase in molecular mobility associated with the surface layers of the roughened solid phase.

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Additional Information:© 1989 American Chemical Society. Received October 27, 1988. We thank Dr. R. Housley for many helpful discussions. This work was supported by DOE contract no. DE-FG03-85ER45192.
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Department of Energy (DOE)DE-FG03-85ER45192
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Record Number:CaltechAUTHORS:20151216-095250085
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Official Citation:Wetting and melting in a methane/graphite system M. S. Pettersen, M. J. Lysek, and D. L. Goodstein Langmuir 1989 5 (3), 563-566 DOI: 10.1021/la00087a004
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:62974
Deposited By: Ruth Sustaita
Deposited On:16 Dec 2015 19:57
Last Modified:10 Nov 2021 23:09

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