Thermal and thermomechanical behavior of polymers

Composites have been prepared based on polymers (epoxy, silicone, and polyurethane) and metal powders (Co and Ni). The composition and the quality of these materials were characterized by densimetry and microscopies (optical and electronic). The study of the variation in electrical resistivity as a function of the volume percentage of the load was carried out in direct current. The electrical resistivity decreases drastically when the percentage of the load increases and in the vicinity of a certain critical concentration (conduction threshold), a sudden drop was observed corresponding to the transition from an insulating state to a driver. The value of the conduction threshold strongly depends on the nature of the constituents. All the results obtained were interpreted within the framework of the theory of percolation. The behavior of electrical resistivity with temperature has also been studied. The PTC (Positive Temperature Coefficient) effect has been demonstrated, when, at a transition temperature called the switching temperature Tc. Correlations between the nature of the matrices and the characteristics of the CTP effect (existence, position, amplitude).