Design and Develop Dielectric Polymers and Nanocomposites of High Energy Density and low losses with High Thermal Stability

The objective of this proposed project is to address the Navy~s future pulsed power, power conditioning, and energy storage needs. Scalable dielectric material and film technologies are desired with significantly increased storage capacity at the device level while maintaining the high cycle efficiencies/low losses of current state-of-the-art capacitors. Polymer dielectrics andnanocomposites based on them have great potential to meet the Navy~s future pulsed power, power conditioning, and energy storage needs. In past a couple of years, we have discovered and been developing a new class of dielectricpolymer nanocomposites. In contrast to the conventional dielectric polymer nanocomposites in which high dielectric constant inorganic nanofillers in high volume loading (more than 10 volume percent) are added to the polymer, we pursue nanocomposites in the opposite, by adding very low volume content (less than 0.5 volume percent) nanofillers to the polymer. We show that in high temperature (high glass transition temperature) dipolar polymers, this new approach can generate a dielectric constant enhancement of more than 50 percent while the nanocomposite films maintain low loss. We further show that by invoking trapping and scattering of crystalline/amorphous interfaces to mobile charges, these high temperature dipolar polymers can achieve a marked enhancement in both the dielectric constant and breakdown strength. For example, a high temperature semi-crystalline dipolar polymer can reach a discharged energy density of more than 27 J/cc under 900 MV/m, which is more 3.3X enhancement in the discharged energy density compared with the base polymer. In addition, such a large enhancement in the dielectric performance is achieved with a very low cost fabrication process, due to very low volume content of nanofillers such as Al2O3 and SiO2, which by themselves are inexpensive, in the nanocomposites. In this ONR program, we propose to carry out a systematical investigation and develop fundamental understanding of the mechanisms which underpin the observed enhancement in thisnew class of dielectric polymer nanocomposites. Nano-probes will be employed to characterize the spatial variation of dielectric and other properties in composite films. Broad band dielectric spectroscope to frequencies above 10 GHz will be used to probe the changes in both dipoles and dipole coupling with the environment in these nanocomposites. Making use of these nanocomposites, we will also investigate how to mitigate the conduction losses at high electric field and high temperature and consequently enhance the dielectric breakdown strength. In viewing of large family of the commercially available high temperature dipolar polymers with different molecular structures, this class of dielectric polymer nanocomposites opens up a totally new approach to realize scalable dielectric polymers with high operating temperature, high energy density, low loss and low cost for Navy and DoD applications. The science developed in this ONR program will pave the way for generating dielectric polymers and devices with unprecedented high performance.