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dc.contributor.authorDiama, Armand, 1965-eng
dc.contributor.authorMatthies, Blake E. (Blake Edward), 1968-eng
dc.contributor.authorHerwig, K. W.eng
dc.contributor.authorHansen, Flemming Y.eng
dc.contributor.authorCriswell, Leah, 1971-eng
dc.contributor.authorMo, Haiding, 1969-eng
dc.contributor.authorBai, Mengjuneng
dc.contributor.authorTaub, Haskelleng
dc.date.issued2009-08eng
dc.descriptiondoi:10.1063/1.3212095eng
dc.description.abstractWe 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.eng
dc.description.sponsorshipThis work was supported by U.S. National Science Foundation under Grant Nos. DMR-0411748 and DMR-0705974.eng
dc.identifier.citationJ. Chem. Phys. 131, 084707 (2009eng
dc.identifier.issn0021-9606eng
dc.identifier.urihttp://hdl.handle.net/10355/8681eng
dc.publisherAmerican Institute of Physicseng
dc.relation.ispartofMissouri Research Reactor publications (MU)eng
dc.relation.ispartofcommunityUniversity of Missouri-Columbia. University of Missouri Research Reactor Centereng
dc.subject.lcshAdsorptioneng
dc.subject.lcshCrystallographyeng
dc.subject.lcshGraphiteeng
dc.subject.lcshCrystal latticeseng
dc.subject.lcshMolecular dynamicseng
dc.subject.lcshMonomolecular filmseng
dc.subject.lcshNeutrons -- Diffractioneng
dc.subject.lcshOrganic compoundseng
dc.titleStructure and phase transitions of monolayers of intermediate-length n-alkanes on graphite studied by neutron diffraction and molecular dynamics simulationeng
dc.typeArticleeng


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