Dielectric properties and morphology of polymer composites filled with dispersed iron

The dielectric properties and the structure of various metal-polymer composites, based on a polymer matrix of polyamide (PA), polyethylene (PE), polyoxymethylene (POM), or blend PE/POM filled with dispersed iron (Fe) particles, have been investigated in this work. In PE-Fe, PA-Fe, and POM-Fe composites the filler spatial distribution is random. In the PE/POM-Fe composites, the polymer matrix is two-phase and the filler particles are localized only in the POM phase, resulting in an ordered distribution of the dispersed filler particles within the blend. The concentration and frequency dependence of the dielectric permittivity, epsilon', and the dielectric loss tangent, tandelta, are described in terms of the percolation theory. The experimental values of the critical exponents (namely, s, r, and y) are in good agreement with those predicted by the theory for the composites with random filler distribution. The PE/POM-Fe composites demonstrate low value of the percolation threshold, P,, and high values of the critical exponents r and y. This is attributed to the specific structure of these composites. A schematic model for the morphology of the composites studied has been proposed. This model explains the peculiar behavior of the PE/POM-Fe composites by assuming ordered distribution of the filler particles in a binary polymer matrix. The proposed model is in good agreement with the results of optical microscopy. (C) 2003 Wiley Periodicals, Inc.