Properties of ferroelectric polymers under high pressure and shock loading

Abstract

Ferroelectric polymers are the most recent class piezoelectric and pyroelectric materials developed. The most common piezoelectric polymers are PVDF, based on the monomer CH 2CF 2 and copolymers PVDF with C 2F 3H. The effects of frequency, temperature and hydrostatic pressure on the dielectric properties, molecular relaxations, and phase transitions of PVDF and a copolymer with 30% trifluoroethylene will be discussed. Pressure causes large slowing down of the β molecular relaxations as well as large increases in the ferroelectric transition temperatures and melting points, but the magnitudes of the effects are different for the different “transitions”. A unique application of these polymers as time-resolved dynamic stress gauges based on PVDF studies under very high pressure shock compression is discussed. In particular piezoelectric response of shock compressed PVDF film prepared with attention to mechanical and electrical processing exhibits precise, well defined reproducible behavior to 35 GPa. P(VDF-TrFE) copolymers exhibit unique piezoelectric properties over a wide range of temperature depending on the compositions. Under high shock pressure loading, unique piezoelectric response is also observed. The first record of detonation profile is presented. Results of PVDF shock sensors subjected to X-ray deposition and to neutron fluence above 10 13 n/cm 2 while stressed at a peak level of 2 GPa will be also discussed.