Thermally stable dynamic piezoelectricity in sandwich films of porous and nonporous amorphous fluoropolymer

Porous amorphous fluoropolymer films of very low stiffness were produced by a solvent evaporation technique. Corona-charged sandwich films consisting of a porous and a nonporous layer exhibit piezoelectric thickness-extension resonances in their dielectric spectrum, through which the temperature dependence of their dynamic stiffness, coupling factor, and piezoelectric coefficient could be determined. Their strong piezoelectricity with coefficients of up to 600 pC/N at temperatures of at least 120 degreesC could make these polymer electret films interesting candidates for sensor and actuator applications in elevated temperature environments. (C) 2001 American Institute of Physics.