Matrix-dependent percolation and resistivity versus temperature behaviors of conducting composite thin films

The surface resistivity of crosslinked polymer matrix conductive ceramic filler composite thin films was studied as a function of composition and temperature. Epoxy resin and unsaturated polyester resin were selected as the insulating matrices. The resistivities of both thin films showed a percolative conduction, and the critical percolation threshold values of the filler weight fraction depended on the type of insulating polymer. The epoxy composite film exhibited a pronounced positive-temperature-coefficient-of-resistivity (PTCR) effect above the glass transition temperature of the matrix. In contrast, the unsaturated saturated polyester composite did not show such an effect. To examine the nature of the percolation and the resistivity versus temperature behavior, the adhesive strength measurements and thermomechanical analysis were conducted on the matrix polymers. The results suggest that the percolation behavior and the occurrence of the PTCR effect in conductor-filled crosslinked polymer composites can be more precisely calculated by taking into account the thermomechanical interaction factor of the components.