Structure–property relationship in nanostructures of young and mature soot in premixed flames M. Alfe ` a , B. Apicella a , R. Barbella a , J.-N. Rouzaud b , A. Tregrossi a , A. Ciajolo a, * a Istituto di Ricerche sulla Combustione – CNR, P.le V. Tecchio, 80, 80125 Napoli, Italy b Laboratoire de Ge ´ologie, Ecole Normale Supe ´rieure, 24 Rue Lhomond, 75231 Paris Cedex 05, France Abstract 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 semi- quantitative 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 nano- structure 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. Ó 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved. Keywords: Soot; Premixed flames; HRTEM; Oxidation; H/C 1. Introduction Structural differences at a nanoscale level of soot (i.e. dimension and orientation of the gra- phitic layers) have been found to affect its reactiv- ity [1] in dependence on fuel and synthesis/ combustion conditions, by means of transmission electron microscopy (TEM) [1–4]. Moreover, it has been speculated that peculiar nanostructures as amorphous and shell/core nanostructures are implicated in the soot formation processes [5]. The amorphous nanostructures are related to soot particles and have been mainly identified in imma- ture soot particles and condensed species [6–8]. The amorphous structures are disordered and iso- tropic throughout whereas the shell–core nano- structure refers to particles in which graphene layers are oriented parallel to the external surface in an outer shell (concentric nanostructure), but are randomly oriented in a central core region [9,10]. The study of soot nanostructures appears thus important for both getting information on 1540-7489/$ - see front matter Ó 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved. doi:10.1016/j.proci.2008.06.193 * Corresponding author. Fax: +39 81 5936936. E-mail address: ciajolo@irc.cnr.it (A. Ciajolo). Available online at www.sciencedirect.com Proceedings of the Combustion Institute 32 (2009) 697–704 www.elsevier.com/locate/proci Proceedings of the Combustion Institute