Conductivity and percolation in epoxy resin/conductive filler composites

Abstract

Composites of the polymer/filler type, when the filler is a conductive material such as metal particles, exhibit electrical conductivity that increases with concentration of the conductive phase. These complex materials are considered to be chaotic mixtures of conductive particles randomly distributed in an insulating matrix. The conductivity of these materials in dc electric fields is studied in terms of percolation theory, where electrical conductivity σ is rapidly increased at a critical concentration, defined as P _c, of the conductive phase, according to σ≈(P­P _c)^α. In this work, various epoxy resin/conductive filler composites were prepared. The filler was metal powder of copper, aluminium, or zinc. The conductive behaviour of these materials was studied at temperatures varied from 20 to 140°C. Data obtained from these measurements are analysed using percolation theory and introducing new parameters β and σ_c into the above relation. A semiempirical algorithm is introduced for the determination of α, β, σ_c, and P _c.