Fabrication And Properties Of Silver/Polyimide Nano-composite Films

The development of modern electronic technology puts forward higherrequirements of embedded capacitor. Dielectric materials with high dielectricconstant, low dielectric loss and outstanding processability are the mostimportant factors in preparation of high-performance embedded capacitor. Thetraditional ferroelectric ceramic/polymer composites have poor mechanicalproperties due to their high filler content, which seriously limits their applicationin the embedded capacitor. Therefore, the development of new dielectricfunctional composite materials with excellent dielectric properties andmechanical properties has become one of the keys in the field of engineeringdielectric materials research.One-dimensional Ag nanorods and three-dimensional Ag nanocubes weresynthesized via ethylene glycol reduction method respectively. By adjusting thereaction conditions, Ag nanorods and Ag nanocubes were achieved in high yield.SEM, XRD, and TEM have been employed to characterize the differentdimensional Ag nanoparticles. Results showed that, the average length anddiameter of Ag nanorods with pentagonal cross-section were8μm and270nmrespectively. The aspect ratio of Ag nanorods was over30. The three-dimensionalAg nanoparticles were nanocubes in morphology with an average diameter of310nm. Growth kinetics analysis showed that, one-dimensional Ag nanorodswere evolved from decahedron intermediate which grown from multiple twinnedAg seeds, while the three-dimensional Ag nanocubes were grown from single-crystal seeds.On this basis, the as-synthesized Ag nanoparticles with differentmorphology were doped into polyamic acid to prepare Ag/PI composite films byin-situ polymerization. A series of Ag/PI composite films with different Ag massfraction were synthesized by thermal imidization. The microstructure, mechanical properties, thermal performance and electrical properties of Ag/PIcomposite films were tested and analyzed. Results showed that, one-dimensionalAg nanorods were homogeneously and effectively dispersed in PI matrix. Whenthe mass fraction of Ag nanorods is6%, the tensile modulus, tensile strength,and elongation at break of the composite film were2.15GPa,110.25MPa, and17.55%, respectively. TGA results showed that, the thermal stability of Agnanorods/PI composite films was nearly in the same with pure PI. Broadbanddielectric spectroscopy results showed that the introduction of Ag nanorodsincreased the dielectric permittivity obviously, but maintained a low dielectricloss when the frequency was lower than105Hz. In the low frequency region, theAC conductivity of composite films exhibited slight increasing trend with theincrease of mass fraction of Ag nanorods, and increased rapidly with increasingthe frequency. Three-dimensional Ag nanocubes had good compatibility with PImatrix and had no aggregation. Introduction of three-dimensional Ag nanocubesdestroyed the partially ordered structure of PI molecular, reducing the arraydensity of PI molecular chain, which led to the slight decrease of mechanicalproperties of composite films. When the mass fraction of Ag nanocubes less than8%, the electrical breakdown field strength was between72.56kV/mm and160.21kV/mm, the volume resistivity was from1.39×109·m to5.72×109·m.Due to the interfacial polarization, the introduction of three-dimensional Agnanocubes increased the dielectric permittivity of the Ag/PI composite films. Thedielectric permittivity of the composite film with mass fraction of8%was morethan4at the frequency range from10Hz to2×106Hz. The dielectric loss of theAg nanocubes/PI composite films was less than0.04at the frequency range from10Hz to105Hz and independent of frequency.