The morphology and properties of polyimide composite films with Ag@Al2O3 nano-particles as fillers

Matal/oxide nanoparticles with a core-shell structure are of essential importance in theoretical sense and practical application in photocatalysis and dielectric materials. In this work, a novel core-shell structural Ag@Al₂O₃ nanoparticle with aluminum oxide as the covering shell and silver as the inner core was respectively synthesized by one-step method and the modified Stöber method. The morphology and structure of the particles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-visible spectroscopy. All the results proved that the Ag@Al₂O₃ nano-particles had a typical core-shell structure, for Al₂O₃ coated Ag particles and the sizes of Ag@Al₂O₃ particles were all in nanometer level. However, the micrographs of the coated particles revealed that particles obtained in the one-step method distributed more uniformly and the size was smaller than that of the ones prepared via modified Stöber method. Then, the obtained Ag@Al₂O₃ nano-particles were doped into the polyimide to fabricate the PI/Ag@Al₂O₃ composite films via an in-situ polymerization process, in which the content of Ag@Al₂O₃ nano-particles was 8wt.%. The morphology, mechanical, thermal and dielectric properties of composite films were investigated. Results showed that the Ag@Al₂O₃ nano-particles dispersed in polyimide matrix homogeneously with nanoscale. With the incorporation of Ag@Al₂O₃ particles, the breakdown strength and the thermal stability of the resultant nano-composite films increased, while the mechanical properties decreased slightly.