Faculty Publications


Different melting behavior in pentane and heptane monolayers on graphite: Molecular dynamics simulations

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Journal/Book/Conference Title

Physical Review B - Condensed Matter and Materials Physics






Molecular dynamics simulations are utilized to study the melting transition in pentane (C5 H12) and heptane (C7 H16), physisorbed onto the basal plane of graphite at near-monolayer coverages. Through use of the newest, optimized version of the anisotropic united-atom model (AUA4) to simulate both systems at two separate coverages, this study provides evidence that the melting transition for pentane and heptane monolayers are significantly different. Specifically, this study proposes a very rapid transition from the solid crystalline rectangular-centered (RC) phase to a fluid phase in pentane monolayers, whereas heptane monolayers exhibit a transition that involves a more gradual loss of RC order in the solid-fluid phase transition, accompanied by uniaxial motion of sublattices and molecules within sublattices. Through a study of the melting behavior, encompassing variations where the formation of gauche defects in the alkyl chains are eliminated, this study proposes that this melting behavior for heptane monolayers is a result of less orientational mobility of the heptane molecules in the solid RC phase, as compared to the pentane molecules. This idea is supported through a study of a nonane monolayer, which gives the gradual melting signature that heptane monolayers also seem to indicate. The results of this work are compared to a previous experiment over pentane and heptane monolayers and are found to be in good agreement. © 2006 The American Physical Society.

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