UCLA

Multifunctional composite materials were developed to enhance the dielectric properties of an epoxy polymer by reinforcing it with ceramic barium titanate (BaTiO₃) particles. Potential applications for this material include structural capacitors that can be used to replace discrete capacitors, currently used for power conditioning or electrical discharge in military systems, giving rise to a reduction in system mass, and cost. BaTiO₃ particles with an average size of 100 nm (cubic) and 200 nm (tetragonal) were used as the filler and EPON^TM Resin 862 (diglycidyl ether of bisphenol F) was used as the matrix. Two parametric studies were performed using Taguchi's Design of Experiments methods. The parameters varied were the volume fraction (V_f) of the particles; the particle size (crystal structure); and the use of dielectrophoretic assembly (DPA), by applying an electric field during the composite curing process. For Study 1, DPA was applied in the plane of the composite mold, and for Study 2, DPA was applied through the plane of the composite mold. The failure stress, FS; Young's Modulus, E; dielectric constant,ε_r, and dielectric loss, tanδ, were characterized and a signal-to-noise ratio analysis was conducted to determine the optimum combination of manufacturing parameters. For Study 1, to maximize FS, the optimum combination was 25% V_f, 100 nm (cubic) particles, and no DPA. To maximize E and &epsilon_r the optimum combination was 50% V_f, 200 nm (tetragonal) particles, and no DPA. To minimize tanδ, the optimum combination was 50% V_f, 100 nm (cubic), and with DPA applied. For study 2, to maximize FS, and to minimize tanδ, the optimum combination was 25% V_f, 100 nm (cubic) particles, and no DPA. To maximize E and &epsilon_r, the optimum combination of parameters was 50% V_f, 200 nm (tetragonal) particles, and no DPA. For both studies, the optimum combination of parameters was determined through statistical methods, and supported by the physics which govern the material properties. A numerical simulation calculated the magnitude of the electric field inside the composite, and the charge on the surface of the material. The simulation and experimental results were in good agreement.