Tuning the crystalline phases of poly(vinylidene fluoride) for capacitive energy storage applications

Radars, defibrillators, high energy lasers, power inverters in electric vehicles are all applications that require highly efficient capacitors having large discharged energy densities in their electronic circuits. Utilizing advanced plastics instead of ceramics as dielectric medium in capacitors offer unique advantages such as flexibility, ease of processing, reliability and, moreover, the ability to withstand high voltages. In this respect, poly(vinylidene fluoride) (PVDF) is an excellent choice to serve as dielectric medium due to its high dielectric constant and high electrical strength, both contributing to high energy density materials. However, at high electric fields PVDF crystals transform irreversible to the ferroelectric crystalline phase, leading to drastically reduced discharged energy densities due to ferroelectric losses. Nevertheless, literature prescribes that these ferroelectric crystals can be beneficial for capacitive energy storage applications when they are well-isolated in nanodomains. In this dissertation, distinct polymeric architectures based on (PVDF) are investigated to optimize the crystallization behavior of PVDF for enhanced dielectric properties. As such, block copolymer self-assembly proves to be a viable method to obtain isolated ferroelectric crystals in nanospheres, while also the temperature dependent crystalline phase transformations of poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-co-TrFE)) copolymers are studied. In the second part of the dissertation, it is discussed that vinyl alcohol (VA) can be incorporated in the PVDF and P(VDF-co-TrFE) backbone, giving ferroelectric P(VDF-co-VA) copolymers and relaxor ferroelectric P(VDF-ter-TrFE-ter-VA) terpolymers. The introduction of VA in the polymer backbone allows these polymers to be crosslinked, leading to novel polymers with appealing dielectric properties. Concerns regarding ferroelectric losses are mitigated, while the discharge energy densities and efficiencies are increased, highlighting the high potential of these materials for capacitive energy storage applications