Piezoelectric properties and temperature stability of poly(vinylidene fluoride-trifluorethylene) copolymers

Abstract

Absfract-Piezoelectric measurements were made on several copolymers of vinylidene fluoride and trifluoroethylene having a vinylidene fluoride concentration in the range of 65 to 75 percent. The hydrostatic g constant showed only a slight dependence on pressure, and pressures up to 35 Megapascal (MPa) caused no apparent loss of the piezoelectric activity. A significant increase in the value of the hydrostatic g constant was observed both at temperatures above and considerably below the room temperature.The anomalous result obtained upon cooling below the room temperature may be attributed to the glass transition temperature of the trifluoroethylene comonomer. Temperature aging studies were performed at high temperatures using films of these copolymers. A significant loss of piezoelectric activity occurred after long-time exposure. Isothermal studies at various aging temperatures revealed that this decay continued over a long time span. The aging behavior characteristically followed a linear dependence on the logarithm of aging time.