Study On The Preparation Organic-vermiculite/PI, Sb-SnO₂/PI Composites And Dielectric Properties

Polyimide (PI) is a kind of high performance material with outstanding thermal, chemical, dielectrical and mechanical properties and has been widely used in the fields of aerospace, microelectronic and cryogenic superconducting field. In Recent yeans, with the rapid development of electronic technology, PIs have been used as substitute of traditional dielectrical materials. But the dielectric constant of pure PI was between 3.0³.5, neither low enough for application in micro-electronic field (below2.5) nor high enough for capacitor application. So, more and more researches focus on the preparation of high dielectric constant or low dielectric constant composites.In this work, organic-vermiculite(OVMT)/PI and Sb-SnO₂ (ATO)/PI composites with lamellar vermiculite and spherical ATO were prepared respectively and their properties were studied in detail.OVMT/PI hybrid films were obtained through monomer intercalating-in situ polymerization method at the presence of modified vermiculite with hexadecyltrimethylammonium bromide.The structure and morphology of OVMT and composite films were studied by scanning electron microscopy (SEM), powder X-ray diffraction (XRD) and fourier transfer infrared spectra (FTIR), and then the mechanical properties, dynamic mechanical properties (DMA), thermal properties and electric properties (dielectric constant and loss factor) of composite films were studied. The results showed that, the dielectric constant of the composite films were all lower than pure PI. The dielectric constant of the composite dropped to 2.56 as the content of OVMT up to 1wt%. The tensile strength and elongation at break were first increased and then decreased with OVMT increasing. The tensile strength increased from 60.98MPa to 92.95MPa with 1.5wt% OVMT content. The temperature at 5.0% weight loss of the composite films were all close to 500℃and could satisfied most demands of dielectric materials.In the preparation of ATO/PI composites, ATO conductive particles were synthesized by chemical precipitation and W/O microemulsion methods and then ATO/PI composite films with different content of ATO were prepared by in-situ polymerization. The ATO particles and composite films were characterized by SEM, XRD, FTIR and then the mechanical properties, thermal properties and electric properties (dielectric constant and loss factor) of the composite films were studied in detail. The results indicated that, the size of ATO particles with narrow distribution prepared by W/O microemulsion method was smaller than that prepared by coprecipitation. The dielectric constant of composites films were almost without change at low ATO content and then increased substantially from 3.79 to 53.38 at 10KHz with the content of ATO increasing from 1.5 wt% up to 3wt%, and then increased to the highest dielectric constant with ATO increasing.