Improved Breakdown Strength and Energy Density in Thin-Film Polyimide Nanocomposites with Small Barium Strontium Titanate Nanocrystal Fillers

Improved dielectric constant, breakdown strength, and energy density are reported for polyimide/sub-10 nm Ba 0.7 Sr 0.3 TiO 3 (BST) nanocomposites up to the percolation threshold. Homogeneous nanocomposites were prepared via an in situ polymerization technique, whereby a suspension of BST is blended with 1,3-bis(4-aminophenoxy)benzene (BAPB) and pyromellitic dianhydride (PMDA) monomers prior to spin-casting and thermal imidization. The dielectric properties the PMDA-BAPB/BST nanocomposites were measured as a function of BST loading and displayed a 24% increase in breakdown strength and calculated energy densities more than twice that of the pure polymer at 10 vol % BST. The PMDA-BAPB/BST nanocomposites also display improved permittivities (ε r = 6.2 at 18 vol % and 1 MHz) and low dielectric loss (tan δ <0.04 for all loadings up to 1 MHz) and are thermally stable above 450 °C in air and 500 °C in nitrogen. The results highlight the benefit of employing extremely small and highly dispersed nanocrystals in capacitive energy storage applications.