(105d) Dielectric Properties of Micro and Nanolayered PC/PVDF Films

There is a need in electronic systems and pulsed power applications for capacitors with high energy density. For large scale capacitor production, advantages of polymers over inorganics include excellent processability and high energy to weight ratio. Current state-of-the-art polymeric capacitors are however limited in that a tradeoff exists between energy density and loss. From a material standpoint, the energy density improves with increasing dielectric constant and/or breakdown strength, whereas the loss may be diminished by reducing dielectric losses and high field polarization hysteresis. Our approach to improve polymer film capacitors is to combine, through microlayer coextrusion, two polymers with complimentary properties: one with a high dielectric constant (polyvinylidene fluoride type polymers - PVDF) and one with a high breakdown strength (polycarbonate). Multilayered films with many alternating layers of polymers exhibited improved breakdown characteristics due to the development of a ?treeing? type failure mechanism.

In addition, a reduction of polarization hysteresis was observed due to layer confinement effects on the solid state structure of PVDF. This work demonstrates that multilayering two polymers synergistically improves the dielectric properties for capacitor applications. Energy densities of up to 13 J/cm3 were measured while maintaining very low losses. Using the understanding gained from these systems, selection and optimization of future layered structures can be carried out to obtain even higher energy densities and lower dielectric losses.