Date of Award
Open Access Dissertation
Harry J. Ploehn
Military and commercial users require next-generation polymer dielectric materials for pulse power and power conditioning applications with rise times less than 1 ms and AC power at frequencies ranging from kHz to MHz. These power density and rate capability requirements necessitate the use of dielectric capacitors that store energy via polarization of electrons in molecular scale dipoles. Multiphase polymer composites and all-polymer dielectrics could be new kinds of materials to meet this acute need for capacitors with compact size and high rate capability.
The polymer nanocomposite (PNC) approach to achieve high energy density employed a “colossal” dielectric constant material, calcium copper titanate, CaCu3Ti4O12 (CCTO) as filler, and high dielectric breakdown strength and low loss polycarbonate (PC) as the polymer matrix. This work systematically analyzes CCTO/PC composites, starting with low field dielectric properties (dielectric constant, dielectric loss) and extending to (for the first time) high field D-E polarization behavior. Our findings suggest that CCTO/PC composites are promising for applications requiring high dielectric constant at low field strength, but not as dielectrics for high density, pulse power energy storage.
“Multiphase all-polymer dielectric” materials is a novel approach to meet the high rate capability demand in dielectric capacitors. Our chemistry collaborators synthesized variety of new homopolymers and copolymers that are hypothesized to form phase-separated, interfacially-dominated structures capable of storing energy through electronic conduction and interfacial polarization. The polymer architecture features a combination of conducting and insulating segments hypothesized to form phase-segregated domains with high electronic conductivity, surrounded by insulating domains that prevent percolation and inter-domain conduction. It is hoped that this method will circumvent shortcomings in existing polymeric dielectric materials for high density energy storage applications. The main result is a terthiophene-containing (PTTEMA) polymer that can store energy density up to 1.54 J/cm3, higher than commercially available biaxially oriented polypropylene (BOPP) at 200 MV/m applied electric field. In addition, different approaches, such as PTTEMA grafted onto barium titanate/PTTEMA composites and PTTEMA/PS polymer blends, have been employed to optimize PTTEMA polymers to make them suitable for pulse power applications. Finally, COMSOLTM simulations were used to understand how polymer composites microstructure affects material polarization.
Islam, S.(2014). POLYMER NANO-DIELECTRICS FOR HIGH DENSITY ENERGY STORAGE. (Doctoral dissertation). Retrieved from http://scholarcommons.sc.edu/etd/2779