TEMPERATURE-DEPENDENT RESISTIVITY AND CONDUCTIVITY MECHANISM IN CARBON PARTICLE-FILLED POLYMERS

The filler-concentration dependence of the room temperature conductivity of epoxy resins filled with various carbon particles is reported: two carbon blacks differing by the particles size and short carbon fibres were used. The familiar insulator-to-conductor transitions are evidenced and analysed according to percolation theory predictions. The temperature variations below room temperature of the resistivity of selected samples are studied. Two distinct temperature dependences are shown, and interpreted as being due either to tunnelling of electrons among neighbouring particles, or to differential thermal expansion of the matrix and the particles when the latter touch one another. All these results are consistent with general results of colloidal stability theories when particles size and shearing (achieved during material processing) are taken into account.