# Reactive Molecular Dynamics Simulations of Polystyrene Pyrolysis
## 2 Results and Discussions
### Tissue Characterization and Carbon Ring Analysis of Pyrolysis Products
#### 2.3.4 Pore Size Analysis  
We analyze the pore sizes and their distribution in the respective pyrolysis products to further differentiate the difference in equilibrium tissues at different target temperatures. The pore size distribution in the equilibrium product at each target temperature is shown in Table 3. The detailed evolution of pore distribution can be found in Figure S6 in the Supplementary Materials.  
According to the previous discussion, we know that the LTs and UHTs contain a large number of discretized fragmented molecules, so the conductivity will not be good. We focus on the better-graphitized PTs and HTS systems. Inside the tissues of these systems, 5-11 A pore size dominates, constituting about 75% of the total. In particular, the 11 A apertures increase while 5-9 A apertures decrease with temperature in the PTs. This phenomenon helps to discern tissue nuances in the PTs. It follows that higher temperatures (3250 K) at PTs favor the formation of materials with wider pore size distributions (PSDs).  
We should note that the theoretical aperture size correlates with the size of the simulated system. Our simulation box is 25.45 A\({}^{3}\); however, the MD simulations of PS pyrolysis  
\begin{table}
\begin{tabular}{c c} \hline
**Temperature (K)** & \(k\)**(s\({}^{-1}\))** \\ \hline
2750 K & 1.94 \(\times\) 10\({}^{8}\) \\
3000 K & 2.51 \(\times\) 10\({}^{8}\) \\
3250 K & 6.16 \(\times\) 10\({}^{8}\) \\
3500 K & 1.06 \(\times\) 10\({}^{9}\) \\ \hline \end{tabular}
\end{table}
Table 2: The rate constant \(k(T)\) for PS pyrolysis by ReaxFF-MD at different temperatures.  
\begin{table}
\begin{tabular}{c c c} \hline
**Temperature** & **Aperture Size** & **Proportion** \\ \hline  & \(<\)5.0 & 9.0\% \\
2500 K & 5.0–9.0 & 44.7\% \\  & 9.0–11.5 & 30.1\% \\  & \(>\)11.5 & 16.2\% \\ \hline  & \(<\)5.0 & 9.1\% \\
2750 K & 5.0–9.0 & 55.4\% \\  & 9.0–11.5 & 27.5\% \\  & \(>\)11.5 & 8.0\% \\ \hline  & \(<\)5.0 & 8.3\% \\
3000 K & 5.0–9.0 & 41.8\% \\  & 9.0–11.5 & 39.9\% \\  & \(>\)11.5 & 10.0\% \\ \hline  & \(<\)5.0 & 8.4\% \\
3250 K & 5.0–9.0 & 40.0\% \\  & 9.0–11.5 & 36.2\% \\  & \(>\)11.5 & 15.4\% \\ \hline  & \(<\)5.0 & 10.0\% \\
3500 K & 5.0–9.0 & 42.0\% \\  & 9.0–11.5 & 32.2\% \\  & \(>\)11.5 & 15.8\% \\ \hline  & \(<\)5.0 & 8.9\% \\
3750 K & 5.0–9.0 & 44.2\% \\  & 9.0–11.5 & 33.6\% \\  & \(>\)11.5 & 13.3\% \\ \hline \end{tabular}
\end{table}
Table 3: Pore size distribution of final equilibrium products at different temperatures. The unit of the aperture size is Å.  
are time-consuming and roughly 15 days were used for one isothermal ReaxFF-MD simulation, so we are unlikely to able to test boxes of different sizes. In fact, what we want to know is the correspondence between the pore size obtained from theoretical simulations and the actual pore size. Therefore, after researching the relevant literature [11], we learned that the aperture size obtained by simulation at the scale of our computational model is roughly 25% of the experimental value. In this way, we can learn the pore size of the actual materials.