Morphology and structure of polymer electrets and ferroelectric polymers

Abstract

Summary form only given, as follows. Most polymers used in electret applications have a semi-crystalline morphology. However, due to the limited diffusion of the large and entangled macromolecules, the crystallization is never complete and crystal growth is limited by topological defects, including possible crosslinks, branches or aretic and atactic sequences. This peculiar crystallization process produces tiny lamellar-crystals, which are embedded in an amorphous matrix. These polymeric materials are thus intrinsically composite and their electrical and mechanical properties depend on the degree of crystallinity as well as on the morphology of the mixed phases. The microstructure of a few polymer electrets was examined, and the charge-transport phenomena in the amorphous region were considered in terms of the nature of the carriers and of the mobility of the chains. Ferroelectric polymers 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 whose time scale can be very short with respect to characteristic times of carrier-diffusion. >