Molecular dynamic simulation of layered graphene clusters formation from polyimides under extreme conditions

The previous experimental study illustrated that a direct laser scribing on polyimide (PI) induced layered graphene, which opened a new door of producing graphene associated materials. However, the underlying conversion mechanism is unknown, especially from theoretical perspectives. In this paper, we performed molecular dynamics (MD) simulation of this mechanism under extreme conditions of high pressure and temperature which mimic those generated by laser induction. We investigated this process using the ReaxFF potential in a nanosecond time scale. We found out that at a pressure of ∼3 GPa and temperature of >2400 K generated from NVT processes, layered graphene clusters were crystallized from PI without metal catalysts, which is consistent with previous experimental results. However, if simulated under NPT processes with a pressure of 27 MPa, the PI was decomposed into small molecules, and no graphene layers were observed. Furthermore, by analyzing the number of the carbon rings and the pair distribution function of them we quantified the crystallinity of the graphene clusters. Through tracing the emission of the small molecules such as H2O, N2, H2, CO we propose possible reaction paths for both of the NVT and NPT processes.