Improved dielectric breakdown strength using bimodal functionalized silica nanoparticles

Nanodielectrics, or dielectric polymer nanocomposites, can exhibit significant improvements in voltage endurance and dielectric breakdown strength compared to unfilled polymer. This work takes advantage of the large interfacial area between the matrix and the filler as a means to introduce chemistry that can further tailor the dielectric properties of the composite. Our studies show that particle dispersion as well as surface group chemistry contributes to property optimization. The large surface to volume ratio of the filler can be detrimental to dispersion as it can promote agglomeration. This obstacle is overcome by grafting polymer chains to the surface of the filler. Reversible addition fragmentation chain transfer, or RAFT polymerization, is utilized to graft polymer chains to the filler surface and control the molecular weight of the grafted polymer. Various electroactive small molecules (terthiophene, anthracene, and ferrocene) were synthesized and attached to the filler surface as well to create a bimodal type architecture. The filler consists of polyglycidyl methacrylate as matrix compatible long chains and short electroactive groups covalently attached to 15nm silica nanoparticles. The dielectric properties were shown to be altered depending on the nature of the surface group and the extent of dispersion. Using dielectric spectroscopy it was found that permittivity and dielectric breakdown strength of the synthesized composites were notably increased with only 2% loading of filler while retaining a level of dielectric loss comparable to the reference matrix