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The silver / polyimide nano dielectric composite material preparation and performance study

Author: LiJun
Tutor: LiHengFeng
School: Central South University
Course: Materials Physics and Chemistry
Keywords: poly(amic acid) polyimide silver nanoparticles chemicalimidization composite particles dielectric properties
CLC: TB383
Type: Master's thesis
Year: 2012
Downloads: 107
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Abstract


Novel materials for embedded capacitor applications are in great demand, for which a high dielectric constant, low dielectric loss and process compatibility with printed circuit boards (PCBs) are the most important prerequisites. To date, no available material meets all these demands and research is needed to further develop materials for embedded capacitor applications. Conductive filler/polymer composites are likely candidate material because their dielectric constants show a dramatic increase near the percolation threshold at a much lower volume concentration of the filler. Silver nanoparticle is a kind of promising filler in view of its supreme electrical conductivity and novel nano-character (i.e. Coulomb blockade effect), and polyimide (PI) as a matrix has excellent performances such as high thermal stability, low dielectric loss and good processability. Therefore, Ag/PI nanocomposites provide an ideal choice to combine the dielectric properties of the silver nano-filler and mechanical, thermal properties of the PI matrix. To achieve high dielectric properties, the Ag/PI composites require utterly uniform dispersion and distribution of the filler in the matrix. However, there are many hot potatoes in the preparation of silver-doped PI hybrids for the big mobility, easy agglomeration and high catalytic activity of silver nanoparticles. Therefore, the study on new fabrication procedure of Ag/PI high-performance composite materials is deserved to be focused on.This work involves two major parts:the in-situ synthesis of silver nanoparticles through the reduction of silver nitrate in the poly(amic acid)(PAA) solution and subsequently the in-situ preparation of Ag/PI nanocomposite particles using the low-temperature chemical imidization method. In the synthesis of silver nanoparticles, surface plasmon resonance (SPR) bands of silver nanoparticles in the PAA solution were monitored with time by UV-vis spectroscopy in order to analyze the crystallization kinetics of silver nanocrystals, which yields Avrami exponents n between0.5and1.5, demonstrating three-dimensional heterogeneous nucleation and diffusion-controlled growth, accompanied with soft impingement effect. Various characterizations, such as TEM, XRD, FT-IR, were carried out to make sure that silver nanoparticles prepared here, as well as the mild and convenient approach illustrated, were beneficial to the following modification of silver nanoparticles and preparation of silver-doped nanocomposites. In the second part, with the aid of the macromolecular coil-like structure of PAA molecules and the interaction between PAA molecules and silver nanoparticles, followed by in-situ low-temperature chemical imidization of PAA, the Ag/PI nanocomposite particles were obtained from the nano-Ag/PAA solution. It was shown that silver nanoparticles could be dispersed uniformly in the chemically-imidized PI matrix without serious agglomeration even after certain thermal treatment (250℃1h). It was the first time to try an all in-situ method to prepare highly silver-contained Ag/PI nanocomposites. There were obvious interfacial polarization responses in the as-prepared Ag/PI nanocomposites, especially under the low frequency (ε’-20@100Hz, about6times higher than that of the PI matrix), indicating the distinct influence of the incorporation of silver nanoparticles on the polarization response of the dielectric system, though there is still a long way to realize the huge dielectric response near the percolation threshold. This experiment may provide a reference for the fabrication procedure of high-performance Ag/PI dielectric nanocomposites in the future.

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