Thermal decomposition of a honeycomb-network sheet: A molecular dynamics simulation study

Abstract

The thermal degradation of a graphene-like two-dimensional honeycomb membrane with bonds undergoing temperature-induced scission is studied by means of Molecular Dynamics simulation using Langevin thermostat. We demonstrate that at lower temperature the probability distribution of breaking bonds is highly peaked at the rim of the membrane sheet whereas at higher temperature bonds break at random everywhere in the hexagonal flake. The mean breakage time τ is found to decrease with the total number of network nodes N by a power law τ ∝ 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 ni of different coordination. The distribution of fragments sizes evolves with time elapsed from initially a δ-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 ni which can be solved exactly and compared to data derived from the computer experiment, providing deeper insight into the thermolysis mechanism.

An Adaptation of the Hoshen-Kopelman Cluster Counting Algorithm for Honeycomb Networks

“…In the course of simulation we calculate properties such as the probability distribution of breaking bonds regarding their position in the membrane, the mean first breakage time of a bond (i.e., the elapsed time until the first bond breakage occurs) depending on membrane size and temperature, the probability distribution of the first breakage time, the mean extension of the bonds in the membrane, as well as other quantities of interest. A detailed description of these measurements can be found in our recent paper [62] where we demonstrated that at lower temperature T = 0.10 the degradation process starts from the rim of the membrane sheet and then proceeds inwards. In contrast, at higher temperature T = 0.15 bonds break at random everywhere in the network sheet.…”

“…In most of these cases, however, mainly a stability analysis is carried out whereas still little is known regarding the collective mechanism of degradation, the dependence of rupture time on system size, as well as the decomposition kinetics, especially as far as 2D polymer network sheets are concerned. Therefore, in a recent work [62] using Molecular Dynamics (MD) simulation we extended the investigations to the case of 2D polymer network sheets, embedded in 3D-space, and studied as a generic example the thermal degradation of a suspended membrane with honeycomb orientation, similar to that of graphene.…”

“…5, one may conclude that even in the case of a homogeneous membrane the thermal degradation process is more adequately described by several reaction constants which govern the dissociation of different groups of bonds. In the recent paper [62] we suggest a simple model of reaction kinetics which takes into account this conjecture. We developed a theoretical scheme based on a set of 1st-order kinetic differential equations, describing the variation of the number of network nodes, connected by a particular number of bonds to neighboring nodes, as time elapses.…”

“…Following Al-Futaisi and Patzek [61], we develop our simplified implementation of the cluster counting algorithm adapted for networks with honeycomb structure. Thereafter we studied the degradation process [62,63] of a two-dimensional membrane model with such honeycomb structure, as shown in Fig. 1.…”

“…We provide a simplified implementation of the Hoshen-Kopelman cluster counting algorithm for honeycomb networks in non-lattice environments. We develop this algorithm to study the thermal decomposition of a membrane with hexagonal shape and honeycomb structure [62] (see Fig. 1).…”