Phase change of polycyclic aromatic hydrocarbon clusters by mass addition

We report the first numerical evidence of the phase change of polycyclic aromatic hydrocarbon (PAH) clusters induced by mass addition using molecular dynamics (MD) simulations. We find that an irregular spherical coronene(50) cluster in the liquid phase is transformed to a columnar particle in the solid phase by coalescing with an identical cluster at 455 K. The evolution of the intermolecular energy and the Lindemann Index are used to monitor the phase change process. The physical reason behind this transformation is the size-dependence of the melting point. We hypothesise that this transformation is a possible mechanism explaining the transition from liquid-phase coalescence to solid-phase fractal growth of soot particles. (C) 2014 Elsevier Ltd. All rights reserved.