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ABSTRACT: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, Ј, and the dielectric loss tangent, tan␦, 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 C , 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.

In the present work broadband dielectric relaxation spectroscopy measurements were employed to investigate the dielectric properties of polymer composites. A polyethylene/polyoxymethylene (PE/POM) thermoplastic blend was used as a matrix, while the inclusions were iron (Fe) particles. For comparison, the two pure polymers‐ PE and POM‐ were used as a matrix, too. 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. In PE‐Fe and POM‐Fe composites, the filler spatial distribution is random. The behaviour of all the composites studied is described in terms of the percolation theory. The PE/POM‐Fe composites, based on the PE/POM blend, demonstrate different electrical behaviour compared to that of POM‐Fe and PE‐Fe systems. The percolation threshold value of the PE/POM‐Fe composites was found much lower than that of the other two systems. The results were related to the microstructure of the composites. A schematic model for the morphology of the composites studied has been proposed. This model explains the peculiar behaviour of the PE/POM‐Fe composites by taking into account the ordered distribution of the filler particles in a binary polymer matrix. Optical microscopy photographs confirm this model.

Structure‐properties relationships of composite materials, consisting of a polymer matrix and metal inclusions, is very important for designing new materials with desirable properties. In the present work the electrical and dielectric properties of several composites, consisting of a polymer matrix and iron (Fe) particles as filler, were investigated. Broadband dielectric relaxation spectroscopy measurements were carried out. The electrical behaviour of the composites is described in terms of the percolation theory. Percolation threshold values were calculated and the values of the dielectric permittivity critical exponent were found in good agreement with the theoretical ones. The influence of using different polymer matrices on the physical properties of the composites was also of particular interest. The results were related to the microstructure of the composites and a schematic model was proposed.