Characterization of PET/PVDF films for high energy density capacitor application.

摘要

The dielectric and electrical breakdown measurements have been conducted on the melt cast and biaxially-drawn PET/PVDF films containing 5, 10 and 30 wt. % PVDF. The biaxially-drawn films containing 5 and 10 wt. % PVDF were found to give the highest electrical breakdown strengths while those containing 30 wt. % PVDF were found to give lower electrical breakdown strengths relative to the pure PET films, 5 and 10 wt. % PVDF films.; It was found that the PVDF particles in the films behaved as physical barriers which obstructed further propagation of electrical tree formations formed during the breakdown process. This partly explains the higher electrical breakdown strength of the 5/95 and 10/90 PET/PVDF films relative to the pure PET films. Another factor such as the excellent ability of the PVDF particles to act as charge (electron) traps was also believed to play an important role in the increment in the breakdown strength of the PET/PVDF films.; An anomalous enhancement in dielectric constant was observed for the 5/95 melt cast films. The dielectric constants for the 5/95 are found to be higher than those of the 10/90 films although the rule of mixtures predicts that this should not be so. The permittivity enhancement is believed to be related to the more extensive interfacial polarization that occurs in the 5/95 film relative to the 10/90 film. It was proposed that electric-field shielding effect may be more prominent in the 10/90 film, which leads to a less extensive polarization of the interfacial charges. With less contribution from the interfacial polarization, the relative permittivity of the 10/90 film is expected to decrease accordingly.; In chapter 6, a reversible crystallite disorientation was observed when a biaxially-drawn PET film was heated above 100°C by X-Ray diffraction. Upon cooling down to room temperature, the original crystallite orientation appeared to be restored. This observed behavior was explained by the uneven coefficient of thermal expansion on the machine and transverse direction of the film.; In chapter 7, the crystal structure of a guanine-based small molecule was investigated by single crystal diffractometer. The existence of covalent interactions such as the intermolecular hydrogen bonding and pi-pi interactions between the molecules can be clearly observed to play an important role in the formation of their crystal structure.