Temperature Dependence of the Structure of Langmuir Films of Normal-Alkanes on Liquid Mercury

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Temperature Dependence of the Structure of Langmuir Films of Normal-Alkanes on Liquid Mercury

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Title: Temperature Dependence of the Structure of Langmuir Films of Normal-Alkanes on Liquid Mercury
Author: Kraack, H.; Ocko, B. M.; Pershan, Peter S.; Tamam, L.; Deutsch, M.

Note: Order does not necessarily reflect citation order of authors.

Citation: Kraack, H., B. M. Ocko, Peter S. Pershan, L. Tamam, and M. Deutsch. 2004. Temperature dependence of the structure of Langmuir films of normal-alkanes on liquid mercury. Journal of Chemical Physics 121(16): 8003-8009.
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Abstract: The temperature dependent phase behavior of Langmuir films of n-alkanes [CH3(CH2)n−2CH3, denote Cn] on mercury was studied for chain lengths 19 ⩽ n ⩽ 22 and temperatures 15 ⩽ T ⩽ 44 °C, using surface tensiometry and surface x-ray diffraction methods. In contrast with Langmuir films on water, where molecules invariably orient roughly surface normal, alkanes on mercury are always oriented surface parallel and show no long-range in-plane order at any surface pressure. A gas and several condensed phases of single, double, and triple layers of lying-down molecules are found, depending on n and T. At high coverages, the alkanes studied here show transitions from a triple to a double to a single layer with increasing temperature. The transition temperature from a double to a single layer is found to be ∼ 5 °C, lower than the bulk rotator-to-liquid melting temperature, while the transition from a triple to a double layer is about as much below the double-to-single layer transition. Both monolayer and bulk transition temperatures show a linear increase with n with identical slopes of ∼ 4.5 °C/CH2 within the range of n values addressed here. It is suggested that the film and bulk transitions are both driven by a common cause: the proliferation of gauche defects in the chain with increasing temperature.
Published Version: doi:10.1063/1.1799993
Other Sources: http://liquids.seas.harvard.edu/peter/2004.pdf/hgalkt_as_published.pdf
Terms of Use: This article is made available under the terms and conditions applicable to Other Posted Material, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#LAA
Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:5028195

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  • FAS Scholarly Articles [7450]
    Peer reviewed scholarly articles from the Faculty of Arts and Sciences of Harvard University
 
 

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