University of Connecticut |
Tuning Dielectric Properties of Ferroelectric Polymers and Polymer Nanocomposites for Electric Energy Storage Friday, November 9, 2007 11:00 am , IMS Room 20 Tuning Dielectric Properties of Ferroelectric Polymers and Polymer Nanocomposites for Electric Energy Storage Qing Wang Department of Materials Science and Engineering The Pennsylvania State University University Park, PA 16802 Dielectric materials are used to control and store charges and electric energies and play a key role in modern electronics and electric power system. Compared to the traditional electroactive ceramics, dielectric polymers enjoy inherent advantages such as high electric breakdown strength, low dielectric loss, easy of processing, and self-healing ability. Polymers with high electric energy density are attractive for applications in electric energy storage with reduced volume, weight and cost, such as stationary power generation and miniature capacitors for telecommunications, portable electronics and hybrid electric vehicles. However, dielectric polymers that are currently used for high energy density capacitors show low dielectric constants (K <3) and thus rely on high electric fields (>500 MV/m) to achieve high energy densities. This talk will describe our efforts to develop new synthetic strategies to polymer based dielectric materials for high energy density capacitors and to understand molecular structure-dielectric property relationships in these materials. We have developed a modular approach toward poly(vinylidene fluoride) (PVDF)-based ferroelectric polymers exhibiting high dielectric constants (K =50 at 1 kHz). This approach allows the chemical compositions of the resulting ter-polymers to be precisely controlled, leading to a library of ferroelectric polymers with tunable dielectric constants and a systematical study of structure-property correlations. An unprecedented energy density (> 17 J/cm3) with fast discharge speed and low loss has been demonstrated in the defect-modified PVDF based copolymers. The introduction of a small amount of disparate chlorinated component, such as chlorotrifluoroethylene (CTFE), into PVDFs induces the change in molecular conformation between the nonpolar and polar forms at room temperature, which is accompanied by a broad and high dielectric response. Our latest studies have shown that a variety of reactive functional groups can be precisely introduced into the PVDF-based ferroelectric polymers, thus opening an exciting research arena where various electroactive nanostructures can be judiciously assembled with predetermined architectures and properties. High energy density ceramic nanoparticles such as rutile TiO2 and BaTiO3 coated with complementary functional groups are incorporated into the ferroelectric polymers with a uniform dispersibility. The effect of nanoparticle structures on dielectric properties of the resulting nanocomposites will be presented.
This seminar is sponsored by a generous grant from U.S. Surgical Corporation |