High Temperature Dielectric Anisotropy of Poly(vinylidene fluoride) Films at Microwave Frequencies

Abstract

Microwave dielectric anisotropy at temperatures between 30°C and 102°C was measured from the determination of the dielectric constant ε′ and loss ε″ at 4.0 GHz for uniaxially stretched poly(vinylidene fluoride) (PVDF) films. The ε′ increased gradually with increasing temperature, whereas ε″ was followed by a sharp upswing with an increase in temperature. These temperature changes in ε′ and ε″ are attributable to the shift of the dielectric α-relaxation swallowing the β-relaxation to high frequency with an increase in temperature. Time dependence studies on ε″ at 4.0 GHz and fixed high temperatures for the uniaxially stretched PVDF film showed a significant decrease in ε″ with time only above ca. 85°C. This phenomenon may be ascribed to the crystallization of PVDF molecules in the amorphous region or the shift of the α-relaxation to high frequency. The dielectric anisotropy for uniaxially stretched PVDF was also identified even at high temperatures.