Abstract
In amorphous copolymer of vinylidene cyanide and vinyl acetate showing high piezoelectricity, a considerable enthalpy relaxation was observed at the glass transition temperature (Tg) by annealing below Tg. The relationships between the excess thermodynamic properties and the piezoelectric properties were elucidated by investigating the effect of isothermal annealing on the depolarization process by the thermal stimulated current (TSC) measurements. From the comparison of activation energies between the enthalpy relaxation and the depolarizing process, the molecular motion associated with the energy absorption in DSC endothermic peak is considered to be the conformational rearrangement of C-CN bond induced by dipole rotations in the glassy matrix. Also corresponding changes in molecular mobility have an influence upon the stability of dipole orientation in depolarizing process. Consequently, annealing below Tg increases the stability of the remanent polarization (Pr) and its corresponding piezoelectricity.
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