Dielectric properties of polyimide/SiO2 hollow spheres composite films with ultralow dielectric constant

In this study, polyimide (PI)/SiO2 hollow spheres (SHS) composite films were prepared by incorporating different contents of 20-50 nm sized SHS into PI derived from pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA). The dielectric constant of the PI films was reduced from 3.41 to 2.09 for a hybrid film containing 10 wt.% SHS. When the content of SHS was >10 wt.%, the dielectric constant increased due to the aggregation of the SHS. The ultralow dielectric constant could be attributed to the presence of air voids within the structure of SHS itself as well as the air between the PI matrix and the SHS. Furthermore, the air content in the PI/SHS composite films was calculated by Bruggeman's Effective Medium Theory. The PI/SHS composite films with ultralow dielectric constant and low dielectric loss can be considered as good candidate for advanced dielectric materials. (C) 2015 Elsevier B.V. All rights reserved.