Towards a predictive model for polycyclic aromatic hydrocarbon dimerization propensity

JS Lowe and JYW Lai and P Elvati and A Violi, PROCEEDINGS OF THE COMBUSTION INSTITUTE, 35, 1827-1832 (2015).

DOI: 10.1016/j.proci.2014.06.142

Soot particles are a significant pollutant formed as the result of incomplete combustion. Particle nucleation significantly impacts the formation and morphology of soot particles, yet remains a key knowledge gap. To elucidate the process of nucleation, we have investigated the thermodynamic stability of dimers of polycyclic aromatic hydrocarbons (PAHs), towards developing a more comprehensive model for PAH clustering behavior. Using a computational methodology based on molecular dynamics and well-tempered Metadynamics, we quantified the impact of morphological parameters on homo-molecular dimerization, as well as the relative size of monomers on the stability of hetero-molecular dimers. The results illustrated the substantial impact of PAH mass and geometry on the stability of homo-molecular and hetero-molecular dimers at flame temperatures. In particular, dimer stability was found to depend most strongly on monomer mass, followed by solvent-accessible surface area. Additionally, hetero-molecular dimer stability was found to be largely determined by the size of the smallest monomer. Identifying relationships between PAH morphology and thermodynamic stability is a significant step towards a more comprehensive understanding of the physical interactions between PAHs. Altogether, this work presents a framework for elucidating the clustering behavior of arbitrary PAHs and will greatly impact understanding and modeling of particle nucleation and growth. (C) 2014 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

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