Dielectric properties of epoxy/Montmorillonite nanocomposites and nanostructured epoxy/SiO2/Montmorillonite microcomposites

Microcomposites are a well known class of materials. The enhancement of polymer matrix properties can be explained by the classical mixing law. But if the inclusion size is decreased to reach the nanometric range, the improvement of properties is no more due to mixing effect but to the influence of interface of nanoparticles on the matrix. A new emerging class of materials is composites reinforced with microparticles using a polymer matrix reinforced by nanoparticles. In order to study dielectric properties of such new materials, epoxy composites have been prepared using quartz as micro filler and organically modified Montmorillonite as nanofiller. Transmission Electron Microscopy has been used to determine the structure of the composites, which is neither exfoliated nor intercalated although the C30B stacks thickness is in the nanometric range. Differential Scanning Calorimetry experiments have been carried out to highlight the nano and microparticles effect on the epoxy matrix amorphous structure. The glass transition temperature is slightly affected by C30B addition but the microparticles inclusion produces a drastic decrease from 357K to 325K. The heat capacity step is rather unchanged except for the microcomposite. And finally, the dielectric properties of the materials have been studied by Broadband Dielectric Spectroscopy at different temperatures and frequencies. The relaxation times and the dielectric strengths associated with local β and γ relaxations and main α relaxation have been studied.