Modelling the self-assembly and structure of carbonaceous nanoparticles

The self-assembly and structure of carbonaceous particles are investigated using molecular modelling methods. This provides a deeper understanding of molecular interactions relevant to pollutant formation and growth in combustion processes and other carbon-based applications. The existing soot particle model, a cluster containing planar pericondensed polycyclic aromatic hydrocarbons (PAHs), is extended to include PAHs of varying sizes. The resulting nanostructures show that the classic core-shell morphology reported experimentally for mature soot particles is not energetically feasible if only considering physical interactions between PAHs. It is proposed that young soot particles present the inverse molecular size partitioning. A detailed survey of the surface properties of heterogeneous PAH clusters is conducted, identifying composition-, size- and temperature-dependent behaviours. A novel stochastic global optimisation method, the Sphere Encapsulated Monte Carlo method, is also developed to allow minimum energy structures of large aromatic systems to be determined at considerably less computational expense than existing methods. The properties of curved PAH molecules are then investigated, and it is hypothesised that their enhanced electronic interactions could play a role in soot particle nucleation. A new intermolecular potential, curPAHIP, is developed to allow the simulation of curved PAHs. Subsequent dynamic clustering studies show that there is a significant increase in particle formation for systems containing curved PAHs and cations, suggesting the importance of these interactions in combustion processes. Further work investigates the structure of clusters containing curved PAHs, and the corresponding influence of cluster size, molecule size and curvature, molecular ratio, and presence of ions. This work develops computational tools useful for examining large systems of aromatic molecules as well as those containing curved species. Detailed studies on nanoparticle nucleation, structure, and surface properties provide valuable information on self-assembly processes crucial to understanding the production and properties of carbonaceous nanoparticles.The Cambridge Trust and King's College, Cambridg

Sphere Encapsulated Monte Carlo: Obtaining Minimum Energy Configurations of Large Aromatic Systems.

We introduce a simple global optimization approach that is able to find minimum energy configurations of clusters containing aromatic molecules. The translational and rotational perturbations required in Monte Carlo-based methods often lead to unrealistic configurations within which two or more molecular rings intersect, causing many of the computational steps to be rejected and the optimization process to be inefficient. Here we develop a modification of the basin-hopping global optimization procedure tailored to tackle problems with intersecting molecular rings. Termed the Sphere Encapsulated Monte Carlo (SEMC) method, this method introduces sphere-based rearrangement and minimization steps at each iteration, and its performance is shown through the exploration of potential energy landscapes of polycyclic aromatic hydrocarbon (PAH) clusters, systems of interest in combustion and astrophysics research. The SEMC method provides clusters that are accurate to 5% mean difference of the minimum energy at a 10-fold speed up compared to previous work using advanced molecular dynamics simulations. Importantly, the SEMC method captures key structural characteristics and molecular size partitioning trends as measured by the molecular radial distances and coordination numbers. The advantages of the SEMC method are further highlighted in its application to previously unstudied heterogeneous PAH clusters

Whatever Happened To ... Feeney?

Article deposited after permission was granted by LRC, June 11, 2013.The article presents an investigation on the case of Michael Feeney and how his case changed the process of police searches and seizures for suspected criminals. It mentions that he was factually guilty of the crime, however, his conviction was overturned since all the evidence which directed towards him has violated his Charter rights. Due to this incident, the government of Canada has amended the Criminal Code to develop a "Feeney warrant" for police searches and seizures..N

Minimum or Reasonable Notice of Termination?

Article deposited after permission was granted by LRC, June 11, 2013.The article discusses the case of both sales personnel Marek and Gilles, which the issue surrounds on the wrongful dismissal in Ontario. It states that the courts list several criteria to determine common law notice to evaluate the action of the company dismissing employees without notice. It explains that the issue was just an accidental error by the employer who was willing to correct by it good faith through paying full legal entitlement.N

Partitioning of polycyclic aromatic hydrocarbons in heterogeneous clusters

The morphologies of heterogeneous clusters of polycyclic aromatic hydrocarbons (PAHs) are investigated using molecular modelling. Clusters of up to 100 molecules containing combinations of the different sized PAHs circumcoronene, coronene, ovalene, or pyrene are evaluated. Replica exchange molecular dynamics simulations using an all-atom force field parameterised for PAHs sample many configurations at high and low temperatures to determine stable low energy structures. The resulting cluster structures are evaluated using molecular radial distances and coordination numbers, and are found to be independent of initial configuration and the cluster sizes studied. Stable clusters consist of stacked PAHs in a core-shell structure, where the larger PAHs are found closer to the cluster core and the smaller PAHs are located on the cluster surface. This work provides novel insight into the molecular partitioning of heterogeneous aromatic clusters, with particular relevance to the structure of nascent soot particles.NRF (Natl Research Foundation, S’pore)Accepted versio

Sphere encapsulated Monte Carlo : obtaining minimum energy configurations of large aromatic systems

We introduce a simple global optimization approach that is able to find minimum energy configurations of clusters containing aromatic molecules. The translational and rotational perturbations required in Monte Carlo-based methods often lead to unrealistic configurations within which two or more molecular rings intersect, causing many of the computational steps to be rejected and the optimization process to be inefficient. Here we develop a modification of the basin-hopping global optimization procedure tailored to tackle problems with intersecting molecular rings. Termed the Sphere Encapsulated Monte Carlo (SEMC) method, this method introduces sphere-based rearrangement and minimization steps at each iteration, and its performance is shown through the exploration of potential energy landscapes of polycyclic aromatic hydrocarbon (PAH) clusters, systems of interest in combustion and astrophysics research. The SEMC method provides clusters that are accurate to 5% mean difference of the minimum energy at a 10-fold speed up compared to previous work using advanced molecular dynamics simulations. Importantly, the SEMC method captures key structural characteristics and molecular size partitioning trends as measured by the molecular radial distances and coordination numbers. The advantages of the SEMC method are further highlighted in its application to previously unstudied heterogeneous PAH clusters.National Research Foundation (NRF)Accepted versionThis project was supported by the National Research Foundation (NRF), Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) program. K.B. is grateful to the Cambridge Trust and the Stanley Studentship at King’s College, Cambridge for their financial support. M.K. gratefully acknowledges the support of the Alexander von Humboldt foundation

Surface properties of heterogeneous polycyclic aromatic hydrocarbon clusters

In this paper we investigate the impact of molecular inhomogeneity on the surface properties of soot particles. Using replica exchange molecular dynamics and solvent-excluded surface analysis, we evaluate detailed surface properties directly from particles containing polycyclic aromatic hydrocarbon molecules of different sizes. The temperature-dependent behaviour of surface roughness and number densities of reactive sites are evaluated for particles from 1-5 nm in diameter. The percentage of carbon atoms and zig-zag sites on the particle surface are found to be independent of molecular composition, while molecule heterogeneity influences the accessible hydrogen atoms and free-edge sites. These relationships allow the prediction of surface composition for a given particle diameter. The surface densities of carbon and hydrogen atoms are explained by the morphological changes and molecule size contributions for solid-like and liquid-like configurations. Small molecules contribute significantly to the particle surface properties at low temperatures, regardless of the proportion of molecule sizes, which results in an increased density of accessible carbon atoms for heterogeneous particles. Interestingly, the surface density of edge carbon atoms and free-edge sites can be predicted from the average molecule size alone. The density of hydrogen atoms on the surface follows the average expected values from the constituent molecule sizes, suggesting that for particles containing many different molecule sizes the alpha parameter corresponding to the HACA mechanism converges to a linear temperature-dependent trend. This quantitative evaluation of the accessibility of reactive sites for heterogeneous particles provides important information for understanding soot particle growth and oxidation.EPSRC (grant number: EP/R029369/1) and ARCHER for financial and computational support as a part of their funding to the UK Consortium on Turbulent Reacting Flows (www.ukctrf.com). The Cambridge Trust and the Stanley Studentship at King’s College, Cambridge. The National Natural Science Foundation of China (No. 51806016) and the Beijing Institute of Technology Research Fund Program for Young Scholars. The National Research Foundation, Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise programme

Exploring the internal structure of soot particles using nanoindentation : a reactive molecular dynamics study

The mechanical properties and internal structure of soot nanoparticles is investigated using reactive molecular dynamics simulations of nanoindenting model soot particles. The particles that are provided as inputs to the simulations are generated using reactive molecular dynamics to create 3D networks of crosslinked coronene, circumanthracene and core-shell mixtures of coronene and circumanthracene. The results of the simulated nanoindentation experiments are analysed as a function of the degree of crosslinking (defined as the number of crosslinks per monomer in the particles), the size and the core-shell structure of the particles. In the case of homogeneous particles (i.e. those without a core-shell structure), the simulations show a unique relationship between the degree of crosslinking (CL) and the simulated hardness, Young's modulus and deformation ratio. In the case of particles with a core-shell structure, a unique relationship was only found by considering the core-shell ratio and the degree of crosslinking in both the core and the shell. Our results allow for interpretation of the nanoindentation experiments as suggesting crosslinks are present in mature soot particles and preliminary evidence that crosslinks also are present within the interior of soot particles.National Research Foundation (NRF)This project is supported by the National Research Foundation (NRF), Prime Minister’s Office, Singapore under its Campus for Research Excellence and Technological Enterprise (CREATE) programme. This project has received funding from the European Union’s Horizon 2020 Research and Innovation Programme under grant agreement no. 724145. The authors are grateful to EPSRC (grant number: EP/R029369/1) and ARCHER for financial and computational support as a part of their funding to the UK Consortium on Turbulent Reacting Flows (www.ukctrf.com)