Piezoelectricity and Pyroelectricity in Crystalline Polymers.
Technical rept. no. 4, 1 Jan-31 Dec 76,
NATIONAL BUREAU OF STANDARDS WASHINGTON D C INST FOR MATERIALS RESEARCH
Pagination or Media Count:
Investigations on piezoelectricity and pyroelectricity in crystalline polymers have been carried out using a copolymer of vinylidene fluoride and tetrafluoroethylene which crystalliezes directly from the melt into a polar crystal form. The crystalline fraction is easily varied from 0.35 to 0.5. Alignment of the dipoles in an applied electric field appears to approach saturation electric fields of 250 kVcm, independent of poling temperatures between 0 and 80 C. Piezoelectric responses from samples of varying crystallinity are consistent with increased polarization and lower compressibility as the degree of crystallinity is increased. Thermal pulse experiments reveal that when poled at room temperature, only a thin region near the positive electrode is poled but the thickness of this region increases with an increase in poling temperature. Copolymer films crystallized from the melt in the presense of a field show greatly improveed stability of piezoelectric activity when stored at elevated temperatures compared with samples poled only after crystallization. The room temperature poling of polyvinylidene fluoride using a corona discharge has been confirmed. Preliminary results are presented which imply that even the non-polar alpha phase of the polymer may be poled in this way but it is unstable--especially at elevated temperatures. Author
- Polymer Chemistry