Melting of hexane monolayers adsorbed on graphite: the role of domains and defect formation

TL;DR

This study uses large-scale molecular dynamics simulations with realistic models to accurately reproduce and analyze the melting transition of hexane monolayers on graphite, revealing molecular reorientation mechanisms and domain structures.

Contribution

First comprehensive large-scale MD simulations of hexane on graphite using realistic models, elucidating the melting mechanism and domain formation.

Findings

Reproduces experimental melting features

Identifies molecular reorientation as the transition mechanism

Discovers domain-type structure in the melted phase

Abstract

We present the first large-scale molecular dynamics simulations of hexane on graphite that completely reproduces all experimental features of the melting transition. The canonical ensemble simulations required and used the most realistic model of the system: (i) fully atomistic representation of hexane; (ii) explicit site-by-site interaction with carbon atoms in graphite; (iii) CHARMM force field with carefully chosen adjustable parameters of non-bonded interaction; (iv) numerous $\ge$ 100 ns runs, requiring a total computation time of ca. 10 CPU-years. This has allowed us to determine correctly the mechanism of the transition: molecular reorientation within lamellae without perturbation of the overall adsorbed film structure. We observe that the melted phase has a dynamically reorienting domain-type structure whose orientations reflect that of graphite.