Piezoelectricity and remanent polarization in vinylidene cyanide/vinyl acetate copolymer

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Abstract
A relationship between piezoelectricity and remanent polarization was obtained from the results of poling experiments on vinylidene cyanide/vinyl acetate, (VDCN-VAc) copolymer. The spontaneous polarization, calculated theoretically from the dipole moment of the copolymer, is about 150 mC/m2. The maximum remanent polarization measured by TSC is 35 mC/m2, less than a quarter of the calculated value. However, this is the largest reported value for an amorphous polymer. The electric field applied to the sample can reverse the remanent polarization due to the C≡N dipole orientation as with ferroelectrics. This was confirmed by a measurement of the dichroic ratio (2200 cm−1) using I.R. spectroscopy. The piezoelectric activity is proportional to the remanent polarization, as given by the relation of e 31 = 1.1e 32 = 0.24e 33 = 0.48Pr (mC/m2). The piezoelectric constant e 33 and the electro-mechanical coupling constant k 33 reveal especially strong activities of 70 mC/m2 and 0.25, respectively, larger than those of poly(vinylidene fluoride). The piezoelectricity of copolymers of vinylidene cyanide and other comonomers was also measured.