Xiaoxu Liu

Influence of interface on the electrical properties of polyimide/TiO 2 composite films

Polyimide/TiO₂ (PI/TiO₂) composite films were fabricated by in-situ polymerization and are reported in this paper. The effect of interface (PI-TiO₂) on dielectric and breakdown properties was investigated via conductivity, photo-stimulated discharge (PSD), permittivity, thermo-gravimetric analysis (TGA) and breakdown characteristic. The results show that interface between PI and TiO₂ in composites contains deep charge traps with density proportional to TiO₂ doping concentration. Interface enhances space-charge polarization to increase conductivity and loss tangent at low frequency. The pinning influence of interface on PI molecular chain motion is reflected in the downtrend of permittivity (0%-4% nano-TiO₂ doping concentration) and increasing decomposition temperature (T_PI<;T_3%<;T_7%). When exposed to corona ageing, the PI matrix rather than interface or nano-TiO₂ is initially damaged, and the remaining mixture of interface and nano-TiO₂ are accumulated gradually on the PI/TiO₂ surface forming a “protective” layer which slowing down further PI/TiO₂ erosion in corona ageing.

Effect of content on dielectric performance of Barium titanate/polyimide films

Polymer-matrix insulating materials are widely used in electrical and electron engineering because of their excellent mechanical properties, thermal and dielectric properties. Barium titanate/polyimide (BaTiO3/PI) nanocomposites have been prepared by an in-situ polymerization process at room temperature. The BaTiO3 phase was observed by scanning electron microscope (SEM), it shows that the BaTiO3 phase was well dispersed in the polymer matrix. The composite with 70 wt% BaTiO3 appears a high dielectric constant of about 15 in the frequency of 103 Hz to 106 Hz and a high breakdown strength of more than 50KV/mm under alternating current (AC) field at room temperature. Meanwhile, the loss tangent of all the simples measured was under 0.015. The volume resistivity of the composite decreased with the increase of the concentration of BaTiO3, but it was still greater than 1.8×1012 ohm-m.

Dielectric properties of PI/BaTiO 3 with disparate inorganic content

Polymer-ceramic dielectric composites have been interesting because they combine the processability of polymers with the desired dielectric properties of the ceramics. Barium titanate/polyimide (BaTiO3/PI) nanocomposite films with high permittivity are prepared by an in-situ polymerization process in this paper. While the mixture contained 70wt% nanosized BT fillers, permittivity of composite film was up to 15.1. In the meantime, the composite possessed the high AC breakdown strength (41MV/m). To be accompanied by the increasing of permittivity, however, other electrical properties of composite materials degenerated slightly, such as dielectric loss and breakdown field strength. The structure of nanoparticles and composites were investigated by means of SEM. The results indicated that barium titanate particles can homogeneously disperse in the PI matrix. A series of composite with high dielectric constant and insulating property were discussed for various filler mass contents.

Preparation and study on the electrical properties of polyimide / TiO 2 hybrid films

Polymer-matrix insulating materials are widely used in electrical and electron engineering owing to their excellent mechanical properties, thermal and dielectric properties. Polyimide/TiO2nanocomoposites have been prepared by the polymerization process of adding nano-TiO2inorganic nonoparticles in polyimide. The structure of nanocomposite films was characterized by FTIR and SEM. The FTIR results confirm the formation of TiO2particles in the PI matrix. The homogeneous dispersion is observed by the SEM, it shows that the phase of TiO2was well dispersed in the polymer matrix. Finally the electrical properties of the PI/TiO2nanocomoposites with nano-TiO2loading from 1%–7% have been investigated. The results show that the breakdown strengths of nano-TiO2 filled polyimide film are deteriorated with the increasing of nano-TiO2 loading, however the breakdown strength reaches its maximum value when the concentration of loading is 1 wt. %. Meanwhile, the relative dielectric constant and the dissipation factor are increased with nano-TiO2loading.

Effect of content on microstructure of PI/TiO 2 hybrid Films

A small-angle x-ray scattering (SAXS) technique using synchrotron radiation as the x-ray source has been employed to characterize the microstructure of PI/TiO2 hybrid films prepared by Sol-Gel method. It is shown that the SAXS profile is hardly constant with Porods law showing a negative and positive slope, suggesting that an interfacial layer exists between the nanoparticles and PI matrix in films when content of more than 5%. This suggests that the inorganic nanoparticles linked to the PI matrix through covalent bond. However, the only positive deviation exists in the film of content 5%. The reason is that there is a fluctuation of electron density in hybrid system. This kind of material has also been proved to possess both surface and mass fractal structures.

Effect of content on dielectric performance of polyimide / TiO 2 hybrid films

In situ polymerized polyimide/TiO2 composite films with good electrical performance are studied. These nanocomposite films are also characterized by scanning electron microscopy (SEM). SEM analyses show that the spherical shaped titania particles and the ceramic particles distribute uniformly in the matrix of hybrid film. Dielectric properties of the films are measured in the frequency range of 102Hz-105 Hz by an impedance analyzer at room temperature. The dielectric constant varies with the sweeping frequency and filler content and it decreases with sweeping frequency. It is demonstrated that the breakdown strength reaches its maximum value when the content of filled TiO2 is 0.5 wt.%, and then decreases with the increase of the concentration of the filler.