Thermal properties of the polypyrrole-poly(methyl methacrylate) (PPy)-(PMMA) compositeswere analyzed by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). A decrease in the glass transition temperatures Tg with the PPy concentration content reveals the increase of segmental motion. Dielectric properties of these composites were studied in the frequency range between 100 Hz and 100 KHz at room temperature for various weight percentage of PPy. The results of the spectra of complex permittivity obey power laws of Jonscher. The values of the exponents n and p are close to 1, which corresponds to a fully correlated system. Key words: Composites, dielectric properties, percolation threshold, conducting polymer.

Dans ce travail, nous nous intéressons aux propriétés diélectriques dans le domaine des micro-ondes (2.45, 9.50 et 35 GHz) des composites constitués des inclusions de noir de carbone dans une matrice résine époxyde. Nous avons utilisé deux types de carbone : le monarch 700 et le sterling, dont les diamètres des inclusions sont respectivement 0.018 et 0.175 μm. Les résultats obtenus montrent que la taille des particules conductrices parait être un paramètre prépondérant pour définir la permittivité complexe de ces composites. Il résulte de cette étude que les modèles proposés pour la détermination de permittivité de ces milieux, devront nécessairement prendre en considération la taille des inclusions.Mots-clés : Lois de mélange, propriétés diélectriques, permittivité complexe,nanocomposites, matrice époxyde, inclusions de carbone.

In this study we present measurements and data analysis of the dielectric relaxation in carbon black (CB) loaded epoxy composites over a wide range of CB concentration (below and above the percolation threshold) and a broad range of frequency (180–1.5×107 Hz). We show that our data are in conflict with the expectation that the fit parameters of the much-discussed two exponent phenomenological percolation equation (TEPPE) represent the critical exponents of the standard percolation theory. This result therefore gives new insight to the problem of why the TEPPE has a limited applicability in representing the effective permittivity versus CB volume fraction functional relationship. We believe that the reason for this discrepancy is that the true dependence of the internal length scales of the mesostructure and the elasticity network is too complicated to fulfill a simple unified functional equation.

ABSTRACT Thermal properties of polypyrrole–polymethylmethacrylate (PPy–PMMA) composites are analyzed by differential scanning calorimetry (DSC). A decrease in the glass transition temperature Tg with the PPy concentration content reveals the increase of segmental motion. The ac conductivity of these composites is studied in frequency range of 600 Hz to 1 MHz and temperature interval 23°C to 110°C. The study depending on the frequency has highlighted three domains: at low frequencies the conductivity is independent of frequency; at intermediate frequencies, the ac conductivity follows a power law in frequency; and at high frequency the ac conductivity can be explained in terms of hopping process.