0 Properties of Nanofillers in Polymer Damien M. Marquis, Éric Guillaume * and Carine Chivas-Joly Laboratoire national de métrologie et d’essais (LNE) France 1. Introduction Polymer nanocomposites have existed for decades, as carbon black, pyrogenic silica and diatomite were used as additives in polymers. Nevertheless, their characterizations and the effect of properties induced by the nanometric scale of fillers was not fully understood at these times. The real starting point, corresponding to an understanding of the action of these fillers, is generally considered as corresponding to the first papers on a polyamide-6 filled with nanoclays published by Usuki et al. (1993) and Okada A. (1995), from Toyota R&D. Both these papers called it "Hybrid" material. Rapidly, research increased, and the first use of the term "nanocomposites" appeared in 1994 [Lan & Pinnavaia (1994), Lan et al. (1995), Giannelis (1996)]. After these pioneers, a lot of researches started on various fillers. The demand for continual improvement in the performances of thermoplastic and thermoset polymer materials has led to the emergence of these new technologies. Nanofillers lists increased within years (nanoclays, nano-oxides, carbon nanotubes, POSS , etc.), as well as the matrix in which they are used and interactions with traditional fillers. Nowadays, the development of polymer nanocomposites is one of the most active area of development of nanomaterials. The properties imparted by the nanoparticles are various and focus particularly on strengthening the electrical conduction and barrier properties to temperature, gases and liquids as well as the possible improvement of fire behaviour. As a method which consists of reinforcing polymer chains at the molecular scale in the same way than the fibres at the macroscopic scale, nanocomposites [Biron (2004), Gloaguen & Lefevre (2007)] represent the new generation of two-phased materials, associating a basic matrix to nanofillers inserted between polymer chains. Nanofillers can significantly improve or adjust the different properties of the materials into which they are incorporated, such as optical, electrical, mechanical, thermal properties or fire-retardant properties, sometimes in synergy with conventional fillers. The properties of composite materials can be significantly impacted by the mixture ratio between the organic matrix and the nanofillers. 2. Classification of nanocomposites 2.1 Terminology Terminology issues were solved recently with standardization. A standardization committee, ISO TC229 "Nanotechnologies", started in 2005, and a joint working group with IEC 113 "Nanotechnology Standardization for Electrical and Electronic Products and Systems" considered terminology and nomenclature issues. This group produced a set of documents * Corresponding author 11 www.intechopen.com