Dipole orientation in the amorphous phase of pvdf by pyroelectricity induced charges

Abstract

The temperature dependence of the pyrocurrent, in poled, bioriented, β-PVDF has been analyzed in the temperature range [-100, 20°C]. The conditions in which the polymer was cooled down across the glass transition, prior to the measurement have been considered. When the sample was cooled under short-circuit conditions, the pyrocurrent increased continuously in the investigated temperature range. After cooling under open-circuit conditions, the spectrum exhibited a peak in the vicinity of the glass transition. This behavior has been interpreted as a kind of TSC signal due to the non-equilibrium between the field of crystalline dipoles, and the field of countercharges localized at the film surface. The magnitude of the resulting macroscopic field increased as the temperature deviated from the reference temperature at which the short-circuit was performed. The TSC peak is due to the return to equilibrium of dipoles of the amorphous phase that have been oriented upon cooling with the macroscopic field.

Key Words:

• PVDF
• pyroelectric charges
• TSC.