Thermal decomposition of a honeycomb-network sheet - A Molecular Dynamics simulation study

TL;DR

This study uses Molecular Dynamics simulations to analyze how a graphene-like membrane breaks down under heat, revealing temperature-dependent bond breakage patterns, kinetics, and fragment size evolution.

Contribution

It introduces a detailed simulation approach and kinetic modeling to understand the thermolysis mechanism of a honeycomb-network sheet.

Findings

Bond breakage is rim-peaked at low T and random at high T.

Mean breakage time scales with network size as N^{-0.5}.

Fragment size distribution evolves from delta to bimodal to single-peaked.

Abstract

The thermal degradation of a graphene-like two-dimensional triangular membrane with bonds undergoing temperature-induced scission is studied by means of Molecular Dynamics simulation using Langevin thermostat. We demonstrate that the probability distribution of breaking bonds is highly peaked at the rim of the membrane sheet at lower temperature whereas at higher temperature bonds break at random anywhere in the hexagonal flake. The mean breakage time $\tau$ is found to decrease with the total number of network nodes $N$ by a power law $\tau \propto N^{-0.5}$ and reveals an Arrhenian dependence on temperature $T$. Scission times are themselves exponentially distributed. The fragmentation kinetics of the average number of clusters can be described by first-order chemical reactions between network nodes $n_i$ of different coordination. The distribution of fragments sizes evolves with time elapsed from a $\delta$-function through a bimodal one into a single-peaked again at late times. Our simulation results are complemented by a set of $1^{st}$-order kinetic differential equations for $n_i$ which can be solved exactly and compared to data derived from the computer experiment, providing deeper insight into the thermolysis mechanism.