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Studies on Structures and Properties of Polyimide/Ag@Al2O3Composite Films

Author: GaoXiaoHui
Tutor: LiuLiZhu
School: Harbin University of Science and Technology
Course: Materials Science
Keywords: polyimide Ag@Al2O3nanoparticls dielectrical propertis
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Type: Master's thesis
Year: 2013
Downloads: 9
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Abstract


In recent years, the high dielectric materials have very important applications in electron, electric and cable industry, especially in the embedded capacitor, due to their predominant role of storage electricity and uniform electric field. Although polyimide has obvious advantages in the high performance dielectric material as it has almost the highest heat resistance in polymer materials, but its dielectric constant is not high and need to be added other fillers to improve its dielectric constant. In order to obtain a new dielectric material with high dielectric constant and low dielectric loss, in this paper, the core-shell structure nano-particles was synthesized and doped as fillers into polyimide to prepare the composite with high dielectric properties.Firstly, a novel core-shell structural Ag@Al2O3nanoparticle was respectively synthesized by one-step method and the modified Stober method. The chemical composition and microstructure of the particles were characterized by UV-visible spectroscopy (UV-Vis), scanning electron microscopy (SEM), fourier transform infrared (FT-IR) and transmission electron microscopy (TEM). The results indicated that the Ag@Al2O3particles obtained in the one-step method distributed more uniformly and the size was smaller than that of the ones prepared via modified Stober method, and some particals with all kinds of sizes can be obtained by changing the mole ratio of Ag and Al2O3, the size of particles decreased gradually as the aluminum ions concentrations increased. The particle size reach the nanometer level when the mole ratio of Ag and Al2O3was1:10and particle size get minimum when that was1:20. FT-IR results showed that there was Al2O3structure in the particles prepared by one-step method. TEM analysis indicated that the sizes of Ag@Al2O3particles reached the nanometer level, Al2O3covered well on Ag and the particles had formed core-shell structure.Based on the in-situ polymerization doping Ag@Al2O3core-shell particles to polyamide acid, a series of doping different particles, different inorganic content and double powders doped composite films were prepared through thermal imiditation. The micro-morphology and structure of composite films were studied by SEM. Results showed that the nanoparticles distributed evenly in the polyimide matrix, and when the content of Ag@Al2O3particles was8wt%, the dispersibility of nano-particles became the best.The dielectric properties, electric breakdown strength, volume resistivity, mechanical properties, the transmittance of UV-Vis and thermal stability of the composite films were tested. Results showed that when the weight ratio of two kinds of particals which the mole ratio of Ag and Al2O3was1:10and1:20respectively, and the total content of inorganic particles was3and8wt%, the composite films showed the highest dielectric constant, which was29.32, and the dielectric loss was only0.0104. Electric breakdown strength of composite films decreased steadily with the increase of the content of inorganic particles. When the inorganic content reached4wt%, the volume resistivity of PI/Ag@Al2O3composite films was the highest among the samples and reached9.26×1013Ω·m, which was26.8%higher than pure PI. Following the increase of content of inorganic particles, the tensile strength and elongation at break of PI composite films had the same change trend, appears to be the trend of decline in turn. UV-Vis transmittance analysis revealed that the transmittance of PI composite films was lower than that of pure PI. TGA analysis showed that the temperature difference between the weight loss at5wt%and10wt%was higher than that of the pure PI. With the further increase of content of Ag@Al2O3particles, a slight increase in temperature difference of the composite film was detected. The result demonstrated that thermal decomposition rate of the composite films became slow, and the thermal stability increased.

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