Interfacial Polarization and its Diagnostic Significance in Polymeric Composites

Abstract

The phenomenon of interfacial polarization appearing in composite materials due to the hindered movement of mobile charge carriers is described. Models of composite dielectrics, including bilayer dielectric, statistical mixtures and matrix-filler type composites are discussed together with theoretical methods used to describe their effective dielectric parameters. Applications of dielectric spectroscopy to polymeric composites are demonstrated using mainly data obtained in the author’s laboratory. Miscibility and phase sepration in polymeric blends can be studied well, as demonstrated for a polyimide/polysulfone blend exhibiting apparent (non-equilibrium) miscibility. Polymer-filler interactions can be monitored in filled/reinforced composites by comparing the glass tansition temperatures of the matrix polymer in neat and in reinforced state. Origin of low frequency polarization processes can also be identified by this comparison. Example is shown for wollastonite and quartz filled epoxies. The effect of adsorbed water, surface treatment on AC dielectric loss and on thermally stimulated currents is shown for CaC03 filled polyolefinic composites. Finally the effect of insulating surface layers in polycrystalline ceramic materials is discussed.