PIEZOELECTRIC POLYMER ELECTRETS

In this review the physical properties, mechanisms and models are revi ewed which explain the high piezoelectricity of the ferroelectric poly mers of the polyvinylidene fluoride (PVDF) family, the odd nylons, the vinylidene cyanide (VDCN) copolymers and polyurea. Because PVDF and i ts copolymers with trifluoroethylene (TrFE) and tetrafluoroethylene (T FE) have been studied extensively in the last 25 years the main part o f the review deals with these polymers. Additionally a short summary o f the different piezoelectric applications of PVDF is presented. The o dd nylons, the VDCN copolymers and the polyurea are compared with PVDF to show the different stabilization mechanisms of the remanent polari zation and the different temperature behavior of the piezoelectricity. This review not only concentrates on the work done in the last few ye ars but in order to describe the behavior of these polymers in detail, it is necessary to go back to the roots. Therefore many articles from the late seventies and early eighties are included.