Epoxy-Silica Nanocomposites: Preparation, Experimental Characterization, and Modeling Federica Bondioli, Valeria Cannillo, Elena Fabbri, Massimo Messori Universita ` di Modena e Reggio Emilia, Dipartimento di Ingegneria dei Materiali e dell’Ambiente, Via Vignolese 905/A, 41100 Modena, Italy Received 17 January 2005; accepted 5 March 2005 DOI 10.1002/app.21854 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Silica nanoparticles having different sizes were obtained by the sol-gel process and characterized. The prepared nanoparticles were subsequently used as reinforc- ing fillers to prepare epoxy-based composites with a silica content ranging from 1 to 5 wt %. SEM analysis and tensile tests carried out on the silica-epoxy nanocomposites indi- cated the absence of particle aggregation and a reinforcing effect in terms of increased elastic modulus. Mechanical properties were also modeled by using a finite element code able to construct a numerical model from a microstructural image of the material. A more reliable model was prepared by considering the presence of an interphase layer surround- ing the particles with intermediate elastic properties be- tween the epoxy and the inclusions and a characteristic size proportional to the particle radius. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2382–2386, 2005 Key words: epoxy resins; mechanical properties; modeling; nanocomposites; silica nanoparticles INTRODUCTION The development of new polymeric materials with improved strength, hardness, and heat resistance rep- resents an important goal from both academic and industrial points of views. In this respect, organic polymers reinforced with nanosized inorganic fillers are very interesting materials, taking into account the dramatic increase in the interfacial area between fillers and matrix, which in turn can significantly improve the overall properties of the polymer. Epoxy resins are widely used in industrial applica- tions thanks to their high mechanical and adhesion characteristics and good solvent and chemical resis- tance, together with their curability in a wide range of temperatures without the emission of volatile byprod- ucts. 1 The properties of epoxy based organic-inorganic composites can be finely tuned by an appropriate choice of the structures of both epoxy prepolymer and hardener and of type and amount of inorganic filler. Several approaches have been proposed 2 for the incor- poration of inorganic structures into organic polymers on a nanoscale: formation of interpenetrating net- works, incorporation of metals and metals complexes in polymers by coordination interactions, intercalation of 2D layered materials or 3D frameworks (zeolites, molecular sieves, etc.), and incorporation of inorganic particles and clusters. As already said, the use of inorganic nanoparticles can be particularly interesting thanks to their easy applicability to the common processing techniques used for epoxy-based conventional composites. In fact, micrometer sized inorganic particles are currently widely used for the reinforcement of epoxy matrices to lower shrinkage on curing and thermal expansion co- efficients, to improve thermal conductivity, and to meet mechanical requirements. The final properties of the composite material are affected by several factors, such as intrinsic characteristics of each component, the content, the shape and the dimension of fillers, and the nature of the interface. 3 Strong interfaces between ma- trix and filler are needed to achieve high perfor- mances, taking into account that the load applied on the composites is mainly transferred to the fillers via the interface. To enhance the properties, smaller size and a larger amount of fillers are required, and in this respect the use of submicron particles can lead to a significant improvement of the mechanical properties of the composite materials. In the last decade, a lot of work has been carried out in the field of preparation of submicron inorganic particles, 4 leading to the possibility of preparing com- posites reinforced with nanofillers. Epoxy resin rein- forced with silica particles having submicron dimen- sions represents one of the most studied systems. Al- ready published results 5–7 evidenced that well- dispersed silica nanoparticles can effectively enhance the comprehensive properties of epoxy-based nano- Correspondence to: M. Messori (messori.massimo@unimore. it). Journal of Applied Polymer Science, Vol. 97, 2382–2386 (2005) © 2005 Wiley Periodicals, Inc.