Conductivity and percolation in polymeric particulate composites of epoxy resin and conductive fillers

Composites of the polymer-filler type, when the filler is a conductive material, show electrical conductivity at a significant volume concentration of the conductive phase and their behaviour can be described in terms of percolation theory. In these heterogeneous systems the constituents have markedly different properties and the ratio of the conductivities of the two components is ~10¹⁰-10²⁰. These systems obey the relation of the percolation theory σ~(P-P_c)^α where σ is the electrical conductivity of the composite material, P is the filler concentration by volume, P_c its threshold value and α the critical exponent. In this work, composites of epoxy resin and metal powders (Cu, Ni, Fe) or carbon black, in various volume fractions were prepared and their DC conductivities were measured. Data obtained by DC measurements are treated using percolation theory and values of P_c and γ are estimated through a suitable algorithm