Effect of fillers on the dielectric properties of polymers

The effect on the permittivity of two different base polymer materials was investigated with two types of fillers. Several theories were investigated to determine which most closely predicted the permittivity of the composites. The fillers utilized were a low permittivity material (alumina) and a high permittivity compound (barium titanate). The base materials investigated were epoxy and silicon rubber. It was found that the permittivity of the alumina filled composite was most closely predicted by the formulae which considered the permittivity of the filler in the calculation, i.e. the log law, Rayleigh´s formula, and effective medium theory. The permittivity of the barium titanate filled materials were most closely predicted by the percolative theories, i.e. Bruggeman´s formula and the effective medium theory, as these materials demonstrated percolative tendencies. The effect of the base material selection on the loss tangent of the filled material was also investigated. It was found that the epoxy samples exhibited little change in the loss tangent over the range of filler levels tested, whereas the silicon rubber samples showed increasing loss tangent with increasing filler level for both the alumina and barium titanate filled samples