Nucleation of fullerenes as a model for examining the formation of soot

Abstract

The formation of soot begins with the nucleation of nanoparticles, a process difficult to model due to the complexity of the constituent particles. Fullerenes have characteristics resembling the particles found in soot, but their simpler structure makes simulations more tractable. We propose that the nucleation of fullerenes may serve as a window to the formation of soot nuclei. Using molecular dynamics simulations, we analyze the nucleation rates of homomolecular systems of C(60), C(80), C(180), and C(240) fullerenes as function of temperature and molecular mass. For temperatures lower than 1000 K, the four systems show similar characteristics, with significant nucleation rates, due to the low energy that favors binding. At higher temperatures, the high kinetic energy limits the binding probability between fullerenes, and molecular clusters are only detected in systems composed of C(180) and C(240). The analysis shows that particles with molecular masses between those of C(80) and C(180) could be critical for the transition from monomers to clusters. The computational findings are then related to experimental data of combustion-generated particles present in the literature to assess the feasibility of a physical nucleation pathway in high temperature regimes. The results obtained using molecular dynamics simulations highlight the importance of a physical nucleation pathway to describe the formation of molecular clusters when the particle concentration exceeds a critical value. These results represent the first step toward a more complete description of nanoparticle formation and soot nucleation in high temperature regimes.