Nonlinear piezoelectricity in oriented films of poly vinylidene fluoride and its copolymers

This study is concerned with experiments on linear piezoelectric properties of PVDF poly(vinylidene fluoride) and its copolymers in the absence of an electrical field. The effect of static stress on the temperature dependence of the piezoelectric stress constant for a copolymer film is presented. Below the glass transition temperature, no stress dependence is detected. A nonlinear behavior occurs if the static stress is applied perpendicular to the chain orientation above the glass transition temperature. This suggests that the nonlinear properties are related to the thermal activation of molecular motions, which take place within the noncrystalline regions as well as interface regions. The nonlinear piezoelectric constant shows relaxation in the glass transition temperature range