Structure and phase transitions of monolayers of intermediate-length n-alkanes on graphite studied by neutron diffraction and molecular dynamics simulation

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Structure and phase transitions of monolayers of intermediate-length n-alkanes on graphite studied by neutron diffraction and molecular dynamics simulation

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dc.contributor.author Diama, Armand, 1965-
dc.contributor.author Matthies, Blake E. (Blake Edward), 1968-
dc.contributor.author Herwig, K. W.
dc.contributor.author Hansen, Flemming Y.
dc.contributor.author Criswell, Leah, 1971-
dc.contributor.author Mo, Haiding, 1969-
dc.contributor.author Bai, Mengjun
dc.contributor.author Taub, Haskell
dc.date.accessioned 2010-10-08T14:28:43Z
dc.date.available 2010-10-08T14:28:43Z
dc.date.issued 2009-08-25
dc.identifier.citation J. Chem. Phys. 131, 084707 (2009 en_US
dc.identifier.issn 0021-9606
dc.identifier.uri http://hdl.handle.net/10355/8681
dc.description doi:10.1063/1.3212095 en_US
dc.description.abstract We present evidence from neutron diffraction measurements and molecular dynamics (MD) simulations of three different monolayer phases of the intermediate-length alkanes tetracosane (n-C24H50 denoted as C24) and dotriacontane (n-C32H66 denoted as C32) adsorbed on a graphite basal-plane surface. Our measurements indicate that the two monolayer films differ principally in the transition temperatures between phases. At the lowest temperatures, both C24 and C32 form a crystalline monolayer phase with a rectangular-centered (RC) structure. The two sublattices of the RC structure each consists of parallel rows of molecules in their all-trans conformation aligned with their long axis parallel to the surface and forming so-called lamellas of width approximately equal to the all-trans length of the molecule. The RC structure is uniaxially commensurate with the graphite surface in its [110] direction such that the distance between molecular rows in a lamella is 4.26 Å = mathag, where ag = 2.46 Å is the lattice constant of the graphite basal plane. Molecules in adjacent rows of a lamella alternate in orientation between the carbon skeletal plane being parallel and perpendicular to the graphite surface. Upon heating, the crystalline monolayers transform to a “smectic” phase in which the inter-row spacing within a lamella expands by ∼ 10% and the molecules are predominantly oriented with the carbon skeletal plane parallel to the graphite surface. In the smectic phase, the MD simulations show evidence of broadening of the lamella boundaries as a result of molecules diffusing parallel to their long axis. At still higher temperatures, they indicate that the introduction of gauche defects into the alkane chains drives a melting transition to a monolayer fluid phase as reported previously. en_US
dc.description.sponsorship This work was supported by U.S. National Science Foundation under Grant Nos. DMR-0411748 and DMR-0705974. en_US
dc.language.iso en_US en_US
dc.publisher American Institute of Physics en_US
dc.relation.ispartof Missouri Research Reactor publications (MU) en
dc.subject.lcsh Adsorption en_US
dc.subject.lcsh Crystallography en_US
dc.subject.lcsh Graphite en_US
dc.subject.lcsh Crystal lattices en_US
dc.subject.lcsh Molecular dynamics en_US
dc.subject.lcsh Monomolecular films en_US
dc.subject.lcsh Neutrons -- Diffraction en_US
dc.subject.lcsh Organic compounds en_US
dc.title Structure and phase transitions of monolayers of intermediate-length n-alkanes on graphite studied by neutron diffraction and molecular dynamics simulation en_US
dc.type Article en_US
dc.relation.ispartofcommunity University of Missouri-Columbia. University of Missouri Research Reactor Center


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