Structure-property relationship in nanostructures of young and mature soot in premixed flames

A structural description of young and mature soot sampled from methane, ethylene, cyclohexane and benzene premixed flames, burning in fuel-rich conditions, was performed by means of high-resolution transmission electron microscopy (HRTEM). HRTEM image analysis was carried out to achieve semiquantitative information about the soot organization. Different nanostructures were found to develop in the soot, depending on the fuel and on soot aging. The soot characteristics were also investigated by elemental analysis, oxidative thermogravimetry and UV-Vis spectroscopy. Soot nanostructure in terms of the length of the graphitic layers, the size of the coherent domains made of stacked layers was related in some way with UV-Vis spectroscopic characteristics, H/C molar ratio, and oxidation reactivity. This demonstrated that there is a structure-property relationship between soot nanostructure and bulk properties. The different spectral features and chemical properties of soot in dependence on the fuel nature and on aging resulted to be related to a different internal structure of primary particles which in turn derives from a different soot inception mechanism occurring in flames more or less rich in aromatic precursors.