POLYMER NANOCOMPOSITES FOR ELECTRICAL ENERGY STORAGE: EFFECT OF STRUCTURING, INTERFACES AND FILLER TYPES
Open Access
- Author:
- Tomer, Vivek
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 14, 2010
- Committee Members:
- C A Randall, Dissertation Advisor/Co-Advisor
Clive A Randall, Committee Chair/Co-Chair
Leslie Eric Cross, Committee Member
Michael T Lanagan, Committee Member
Susan E Trolier Mckinstry, Committee Member
Evangelos Manias, Committee Member - Keywords:
- High Energy Density
Polymer Nanocomposites
Dielectric Breakdown - Abstract:
- Dielectric materials have been widely employed throughout the electrical industry as insulators or capacitors. In recent years, the need for efficient transient energy storage has motivated research for better materials capable of accumulating a large charge per unit volume when compared to current state-of-the-art technology. Although many materials possess either high permittivity or high dielectric strength, it is the combination of the two that is needed for the development of new materials with large recoverable energy storage ~10 J/cc. This thesis is focused on understanding and improving the properties of polymer composites, with high permittivity particulate fillers, that generally su ffer from poor dispersion, large dielectric loss at high fields and exhibit low breakdown strengths. Furthermore, it is shown that the dielectric properties of polymer/inorganic nanocomposites can be enhanced by the achieving better dispersion and designing engineered spatial distribution of the inorganic particulate fillers within the polymer matrix. Dielectrophoretic assembly and shear alignment processes are utilized to create anisotropic composites and study their corresponding electrical properties, i.e., permittivity, dielectric breakdown, and energy density as function of ceramic volume fraction and connectivity. The permittivity and recoverable energy density of composites was found to be highly dependent on the anisotropy present in the system. Experimental results indicate that x-y-aligned (perpendicular to the measuring fi eld direction) composites exhibit higher breakdown strengths along with large recoverable energy densities when compared to 0-3 (random) composites. This demonstrated that engineered anisotropy can be employed to control dielectric breakdown strengths and nonlinear conduction at high fi elds in heterogeneous systems. Furthermore, this thesis investigates the benefits of anisotropic composites with better polymers (Epoxy and PVDF-HFP) and high aspect ratio particulate fillers. We identify the role of interfaces in randomly dispersed biphasic and triphasic composites of organically modifi ed montmorrillonite (OMMT) clay, barium titanate (BaTiO3) and Epoxy. Also, their electrical properties as function of ceramic volume fraction and composite morphology are examined. Final efforts are geared towards development of shear aligned anisotropic nanocomposites with thermoplastics such as linear low density polyethylene and fluoropolymers i.e. poly(vinylidene fluoride hexafluoropropylene) (P(VDF-HFP)) that possess dielectric constant in the range from 10 to 14 (measured at 1 kHz). This thesis conclusively demonstrates that manipulation of anisotropy in high-fi eld dielectric properties can be exploitedfor the development of high energy density polymer-ceramic systems.