MORPHOLOGY AND STRUCTURE OF POLYMER ELECTRETS AND FERROELECTRIC POLYMERS

Most of the polymers used in electret applications have a semicrystalline morphology. This means that they contain crystalline regions in which the chains are closely packed. However, the crystallization is never complete and produces tiny (approximately 50 nm) lamellar crystals, which are embedded in an amorphous matrix. These materials are thus intrinsically composite and their electrical and mechanical properties depend on both the degree of crystallinity and their morphology. In addition, the amorphous phase of semi-crystalline polymers is far less homogeneous than that of glassy or molten polymers. Ferroelectric polymers also have a semicrystalline microstructure, but exhibit different electrical properties because of the spontaneous polarization of the crystalline phase. The microscopic process of their poling thus involves a reorientation of the ferroelectric axes of the crystallites in a time scale which can be very short with respect to characteristic times of carrier diffusion.