Electrical and thermal conductivity of polymers filled with metal powders

The electrical and thermal conductivity of systems based on epoxy resin (ER) and poly(vinyl chloride) (PVC) filled with metal powders have been studied. Copper and nickel powders having different particle shapes were used as fillers. The composite preparation conditions allow the formation of a random distribution of metallic particles in the polymer matrix volume for the systems ER–Cu, ER–Ni, PVC–Cu and to create ordered shell structure in the PVC–Ni system. A model is proposed to describe the shell structure electric conductivity. The percolation theory equation σ∼( ϕ− ϕ c) t with t=2.4–3.2 (exceeding the universal t=1.7 value) holds true for the systems with dispersed filler random distribution, but not for the PVC–Ni system. The percolation threshold ϕ c depends on both particle shape and type of spatial distribution (random or ordered). In contrast to the electrical conductivity, the concentration dependence of thermal conductivity shows no jump in the percolation threshold region. For the description of the concentration dependence of the electrical and thermal conductivity, the key parameter is the packing factor F. F takes into account the influence of conductive phase topology and particle shape on the electrical and thermal conductivity.