Epoxy/Silica Nanocomposites: Nanoparticle-Induced Cure Kinetics and Microstructure Patrick Rosso, * Lin Ye Introduction Over the past decade there have been intensive studies of the development of polymer nanocomposites with nano- meter-sized additives, and these materials have demon- strated their unique properties with improvements in stiff- ness, toughness, and tribological behaviour. [1–3] Epoxy nanocomposites have been extensively investigated for use as adhesives, functional coatings, and packaging mate- rials for electronic devices, and in particular, matrices of advanced fibre composites with improved performance. However, there is still a lack of knowledge about the mechanisms responsible for the dramatic changes in properties. The current procedures for the development of these materials are mostly based on ‘trial and error’ appro- aches, adopting the methods commonly used for micro- meter-sized particulate composites. Fundamental under- standing is very limited in the field and often leads to the conclusion that approaches commonly used for particulate composites are not suitable when a nanometric phase is involved. [4] There have been significant efforts over the past decade to develop modified epoxies with various nano-additives including carbon nanotubes/fibres, exfoliated nanoclays, and organic/inorganic nanoparticles. However, few sys- tems have achieved uniform dispersions of nanoparticles without agglomeration. Recently, a novel nanosilica system was developed by a German company (Nanopox F, nanoresins AG), which can achieve a uniform dispersion Communication This study reveals the influence of silica nanoparticles on the cure reactions of a diglycidyl ether of bisphenol A epoxy resin. As soon as the silica nanoparticles are added to the neat resin (1, 3, and 5 vol.-%), the total degree of conversion increases with an increasing amount of nanoparticles, and the cure reaction shows a more complex autocatalytic behaviour, which can not be described by a traditional kinetic model. Results from subsequent thermo- mechanical analyses confirm an alteration in the microstructure attributable only to the presence of the nanoparticles in the curing stage. An amino-rich interphase around the reactive treated particles is formed, which shifts the resin/hardener ratio, and benefits the homopolymerization of the epoxy and leads to a more highly crosslinked epoxy network. At the same time, the nanophase consists of a core-shell structure with the rigid particle inside and a rubber-like shell because of the excess hardener in this region. P. Rosso, L. Ye Centre for Advanced Materials Technology, School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, NSW 2006, Australia Fax: þ61 2 9351 7060; E-mail: patrick.rosso@aeromech.usyd.edu.au Macromol. Rapid Commun. 2007, 28, 121–126 ß 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/marc.200600588 121