Faculty Publications

Structural And Phase Properties Of Tetracosane (C24H 50) Monolayers Adsorbed On Graphite: An Explicit Hydrogen Molecular Dynamics Study

Document Type

Article

Journal/Book/Conference Title

Langmuir

Volume

24

Issue

21

First Page

12392

Last Page

12397

Abstract

We discuss molecular dynamics (MD) computer simulations of a tetracosane (C24H50) monolayer physisorbed onto the basal plane of graphite. The adlayer molecules are simulated with explicit hydrogens, and the graphite substrate is represented as an all-atom structure having six graphene layers. The tetracosane dynamics modeled in the fully atomistic manner agree well with experiment. The low-temperature ordered solid organizes into a rectangularly centered structure that is not commensurate with underlying graphite. Above T = 200 K, as the molecules start to lose their translational and orientational order via gauche defect formation a weak smectic mesophase (observed experimentally but never reproduced in united atom (UA) simulations) appears. The phase behavior of the adsorbed layer is critically sensitive to the way the electrostatic interactions are included in the model. If the electrostatic charges are set to zero (as for a UA force field), then the melting temperature increases by ∼70 K with respect to the experimental value. When the nonbonded 1 -4 interaction is not scaled, the melting temperature decreases by ∼90 K. If the scaling factor is set to 0.5, then melting occurs at T = 350 K, in very good agreement with experimental data. © 2008 American Chemical Society.

Department

Department of Physics

Original Publication Date

11-4-2008

DOI of published version

10.1021/la802071a

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