(186u) Ion-Induced Nucleation of Carbonaceous Nanoparticles

Ion-induced
nucleation of carbonaceous nanoparticles

Kimberly
Bowal¹, Jacob W Martin¹, Laura Pascazio¹, Markus
Kraft^1,2,3

¹University of
Cambridge, ²Nanyang Technological University,

³Cambridge Centre
for Advanced Research and Education in Singapore

Carbonaceous
particles, known as soot, are by-products of incomplete combustion that
negatively impact combustion devices, human health and the environment. There
is a strong desire to mitigate these undesired effects through the use of clean
fuels or redesign of combustion devices. This requires detailed knowledge of
the complex chemical and physical processes involved in the formation and
growth of soot particles, including the gas-to-solid transition of hydrocarbon
molecules to form soot particles.  This process is poorly understood, largely
due to its low species concentrations, short time frame, and small length
scales, which limit experimental measurements. Molecular modelling tools are
not restricted by these conditions and therefore provide valuable insight into
soot nanoparticles.  It is known that curved polycyclic aromatic hydrocarbons
(cPAHs) possess significant dipole moments and are found within flames [1]. 
Recent work suggests that long-range interactions between these curved species
and chemi-ions may be important to the soot formation mechanism [2].

This
work explores the impact of these ion-dipole interactions in stabilising
nascent soot particles and works towards the development of a heterogeneous
nucleation model for these species. A force field is developed that is able to
capture the flexoelectric effect and enhanced electrostatic interactions. This
is used within advanced molecular dynamics simulations to provide information
on homogeneous and ion-induced heterogeneous nucleation of cPAHs. The
clustering behaviour and resulting morphologies are explored across a range of
temperatures.  These results provide insight into how the interactions between
cPAHs and ions affect the formation and structure of soot nanoparticles and provide
valuable information towards expanding current soot models.

Figure 1: Percent of molecules clustered over time for curved PAH
(corannulene) and planar PAH (coronene) systems, with and without potassium ions
present. Representative cluster images are shown on the right for corannulene
and coronene systems containing ions.

1.       Martin, J. W., Slavchov, R. I., Yapp, E. K.
Y., Akroyd, J., Mosbach, S., & Kraft, M. (2017). Journal of Physical
Chemistry C, 121(48), 27154–27163.

2.       Martin, J.W., Bowal, K., Menon, A.,
Slavchov, R.I., Akroyd, J., Mosbach, S., Kraft, M. (2019). Proceedings of
the Combustion Institute. 37(1), 1117-23.