The electret properties of two kinds of poly(vinylidene fluoride-hexafluoropropylene) copolymer films

P(VDF-HFP) (poly(vinylidene fluoride-hexafluoro-propylene)) copolymer is a new member of PVDF family. In this paper, the electret properties of the two kinds of casting prepared P(VDF-HFP) copolymer films whose content of HFP is 4.7% and 5.9% respectively were discussed with the focus on the influences of mechanically thermal stretching process and of the content of HFP on electret properties of the said copolymer. Experimental results point out that the said copolymer electret film is a polar material, i.e. there exist both oriented dipoles and deposited space charges in the film after charging. The mechanically thermal stretching process not only increases the density of oriented dipoles and deposited space charges but also improves the stability of deposited space charges; however, the increase of HFP content in the copolymer has a negative impact on the density of oriented dipoles and deposited space charges. The measurement result by means of Laser Doppler Vibrometer shows the copolymer in which the HFP content is 4.7% has a notable converse coefficient as high as 130pm/V.