Q.Q. Lei

Preparation of Polyimide/Inorganic Nanoparticle Hybrid Films by Sol–Gel Method

In this study polyimide/inorganic silica–alumina nanoparticle hybrid films are first prepared by sol–gel method to find a promising method for enhancing thermal property and other properties. Silica sol and alumina sol starting from tetraethoxysilicane (TEOS) and aluminum isopropylate (AIP) are doped in a solution of poly (amic acid). The hybrid films are obtained by a stepwise heating method. The structure, micro-morphology, and thermal properties of the films are characterized by Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The micrographs show uniform distribution of club shaped particles in the films containing silica and alumina. The micrographs of polyimide/silica hybrid films revealed sphericity and uniform distribution of particles. Al2O3 particles are poorly dispersed and are prone to agglomerate in the polyimide/alumina hybrid films. Moreover, there are chemical bonds between inorganic and organic phases in the hybrid films. The thermodecomposition temperature of the hybrid films is also improved markedly after the addition of silica and alumina nanoparticles.

Synthesis and characterization of corona-resistant nanocluster-trapped polyimide/silica composites

A new class of corona-resistant films made of nanocluster-trapped polyimide/silica composites that were synthesized by the sol-gel reaction was obtained by the hydrolysis and poly-condensation of tetraethoxysilane (TEOS) or methyl-triethoxysilane (MTEOS) in the solution of polyamic acid(PAA) dissolved in N,N-dimethy-lacetamide (DMAc), followed by heating. The chemical structure and the surface morphology of the composites films were characterized by Atomic Force Microscope (AFM)- and Fourier Transform Infrared Spectroscope (FTIR). The corona-resistant capacity of the composites films was tested under high voltage using rod-plate electrode. The compatibility between the organic phase polyimide (PI) and inorganic phase silica (SiO/sub 2/) had great effects on the properties of PI/SiO/sub 2/ films, especially on their corona-resistant capacity. And this capacity of the Nanocluster-trapped PI/SiO/sub 2/ films increased with increased content of silica.

Ni-coated CaCu3Ti4O12/low density polyethylene composite material with ultra-high dielectric permittivity

We report a novel low-density polyethylene (LDPE) composite filled with nickel-coated CaCu3Ti4O12 ceramic (denoted as CCTO@Ni), prepared by a melt mixing technique, and its prominent dielectric characteristics. The effects of magnetic field treatment on the dielectric properties of CCTO@Ni/LDPE composite films with a low filler concentration of 10 vol.% were investigated. Our results show that the dielectric permittivity, loss tangent, and conductivity of the LDPE composite films initially improved and then decreased with increasing treatment time under the applied magnetic field. Magnetic field treatment for 60 min led to an ultra-high dielectric permittivity value of 1.57 × 104, four orders of magnitude higher than that of the pure LDPE material. Our results indicate that the magnetic treatment may have induced a percolation effect and enhanced the interfacial polarization of the CCTO@Ni/LDPE composite, resulting in the observed changes in its dielectric properties.

Effects of magnetic field treatment on dielectric properties of CCTO@Ni/PVDF composite with low concentration of ceramic fillers

Using melt mixing, we produced a ceramic/polymer composite with a matrix of polyvinylidene fluoride (PVDF) and a filler of 5 vol.% Ni-deposited CaCu3Ti4O12 core-shell ceramic particles (CCTO@Ni), and studied its prominent dielectric characteristics for the first. Its phase composition and morphology were analyzed by X-ray diffraction and scanning electron microscopy, respectively. After treating the composite films with various durations of a magnetic field treatment, we compared their dielectric properties. We found that the CCTO@Ni ceramic had a typical urchin-like core-shell structure, and that different durations of the magnetic field treatment produced different distributions of ceramic particles in the PVDF matrix. The dielectric permittivity of the untreated CCTO@Ni/PVDF composite was 20% higher than that of neat PVDF, and it had a low loss tangent. However, only the composite treated for 30 min in the magnetic field had an ultra-high dielectric permittivity of 1.41 × 104 at 10 Hz, three orders of ...

Improving dielectric properties of PVDF composites by obtaining the BT-Ni particles

In the rapid development of modern science and technology, the dielectric materials with more extraordinary performance were extremely demanded in the electronic system fields. Nowadays, outstanding-performance polymers, which possess a high dielectric constant and flexibility but low dielectric loss have attracted great attention owing to their potential application in many cutting-edge industries, including microelectronics, aerospace, and aviation. In general, the polymers possess excellent flexibility and high breakdown strength, but their applications was limited by the low dielectric permittivity. Numerous efforts have been made to improve the dielectric permittivity of dielectrics by incorporating ceramic additives into polymer matrix. Unfortunately, the high dielectric permittivity needs high filler loading, which causes them to lose their flexibility and decreased breakdown strengths. Herein, the Ni nanoparticles was deposited on the surface of the BT particles to obtain the BT-Ni particles by electroless plating method. The phase composition and morphology were analyzed by X-ray diffraction and scanning electron microscopy, and the effects of BT-Ni filler on the dielectric properties of the composites were investigated in detail. It can be found that the high dielectric permittivity of the composites increased to 61 at 100 Hz when the content of BT-Ni filler was 20vol.%, which is 2.54 times higher than that of 20vol.% BT/PVDF (24) and even greater than that of 40vol.% BT/PVDF (56). The Ni nanoparticles was strong interaction deposited on BT particles, and this structure can effectively suppress the probability of the Ni nanoparticles to form a conductive networks in the PVDF polymer matrix, which can greatly depress the increase of dielectric loss tangent and conductivity of the BT-Ni/PVDF composites. These results indicated that the dielectric constant of the composites can be significantly improved by incorporating Ni conducting particles into the polymer matrix and that the interfacial polarization effect is an important feature of BT-Ni/PVDF composites. This work provides a simple and effective way for preparing nanocomposites with enhanced dielectric properties for use in the electronics industry.

The effect of CaCu 3 Ti 3.95 Zr 0.05 O 12 fillers on microstructure and dielectric behaviour of CaCu 3 Ti 3.95 Zr 0.05 O 12 /Polyimide composites

In the present study, the microstructure and dielectric properties of composites comprising Polyimide (PI) and CaCu3Ti4O12 (CCTO) or CaCu3Ti3.95Zr0.05O12 (CCTZO) particles have been investigated. CCTO and CCTZO were employed separately and investigated comparatively. The effective dielectric constant of the composite containing 40vol.% CCTZO filler is over 50 at 40°C (102 Hz), which is substantially higher than that of the composite containing CCTO. For the composite containing 40vol.% CCTZO, the dielectric constant and the conductivity increases sharply with increasing temperature. The mechanism of high dielectric constant was investigated finally.

Effects of Coupling Agent on Morphology and Properties of Polyimide/ SiO2-Al2O3 Hybrid Films

In this paper, a new type of PI/SiO2-Al2O 3 hybrid film was prepared by sol-gel method. The effects of gamma-aminopropyl triethoxysilane(DB-550) were studied as follows: the micro-morphology of inorganic phase of the films was characterized by Atomic force microscope (AFM); the thermal property of hybrid films was measured by thermogravimetric analysis (TGA) and the breakdown strength was got from breakdown strength apparatus. The results indicated that the participation of quantificational coupling agent (DB-550) produced more chemical bonds between inorganic phase and organic phase, which enhanced the compatibility of two phases. The thermo-decomposed temperature and the breakdown strength of the hybrid films doped coupling agent were all improved