Abstract
Piezoelectricity is observed in films of poly (vinylidene fluoride) (PVF2), poly (vinyl fluoride), poly (vinyl chloride), polycarbonate and nylon 11 when they are elongated and polarized by a static field. The largest value of g31, and d31 found in PVF2 films were 150 millivolts/gram cm and 20×10-8cgs esu respectively. The piezoelectricity of the polymer films is caused by the electrostriction and the spontaneous polarization due to the poling effect. By a newly developed apparatus, electrostrictive constants, inverse piezoelectric constants and their temperature dependence were measured for the polymer films. The electrostrictive constant γ31T of PVF2 film is about 3.5×10-11cgs esu and several times larger than those of other films. The large piezoelectricity of PVF2 is due to the large value of γ31T. It is suggested that the previously reported shear-type piezoelectricity of the natural polymers are caused also by electrostriction and spontaneous polarization.
