Daniel Qi Tan

Computational study of filler microstructure and effective property relations in dielectric composites

Phase field modeling and computer simulation is employed to study the relations between filler microstructures and effective properties of dielectric composites. The model solves electrostatic equations in terms of polarization vector field in reciprocal space using a fast Fourier transform technique and parallel computing algorithm. Composites composed of linear constituent phases of different dielectric constants are considered. Interphase boundary conditions are automatically taken into account without explicitly tracking interphase interfaces in the composites. Various factors associated with filler microstructures are systematically investigated, including dielectric constant mismatch between fillers and matrix, particle size, shape, orientation, volume fraction, and spatial arrangement as well as directional alignment. Heterogeneous distributions of polarization, charge density, and local electric field are calculated for each composite microstructure, based on which effective dielectric constant an...

Computational study of dielectric composites with core-shell filler particles

Phase field modeling and computer simulation is employed to study dielectric composites with core-shell filler particles for high-energy-density applications. The model solves electrostatic equations in terms of polarization vector field in reciprocal space using fast Fourier transform technique and parallel computing algorithm. Composites composed of linear constituent phases (matrix, core, and shell materials) of different dielectric constants are considered. Inter-phase boundary conditions are automatically taken into account without explicitly tracking inter-phase interfaces in the composites. The core-shell structures of filler particles are systematically investigated in terms of shell thickness and dielectric constant with respect to core size and matrix dielectric constant, respectively. The effects of filler particle size, shape, and orientation are considered. It is found that core-shell structures of filler particles provide effective means to mitigate local electric field concentration in diel...

Effect of polar particles on polymer composite dielectrics

Incorporated with polar ceramic particles, polymers were shown to exhibit improved dielectric properties. This work focused on the interaction of polar ceramic particles with the hosting polymers so as to improve the distribution of particles and the dielectric properties of polymer composites. Both computation and experimental observation were conducted toward the understanding of composite dielectric engineering. The electric field was found to be localized at the particle-polymer interface likely contributing to the polarization of polar particles.

Nano-enabled metal oxide varistors

Zinc oxide based metal oxide varistors (MOV) are widely used electrical surge protection components. The design of modern high power, high-density electronic systems necessitate the need for smaller footprint, higher current density and higher nonlinearity MOVs. Such requirements can no longer be satisfied by commercially available MOVs due to their limited voltage capability, high leakage current and mechanical cracking related reliability issues, most of which are associated with the presence of defects and coarse granularity and lack of uniformity in their microstructures. New formulations and processes have been developed to overcome such limitations. This work has developed nano-enabled MOV compositions that can be sintered at relatively lower temperatures than typical commercial MOVs, but with largely improved I-V characteristics due to refined and uniform sub-micron structures. These nano-enabled MOVs show not only high breakdown strength (1.5 kV/mm) with low leakage current, but also a large nonlinear alpha coefficient > 50 at high fields, a measure of the speed of the transition from the insulating to conducting state and the effectiveness of over-voltage protection. A > 10x increase in breakdown strength compared to commercial MOVs, along with much higher nonlinearity, will enable MOV miniaturization, high voltage surge protection, and open up new areas of application.

Nanostructured dielectric materials

This paper presents a progress update with the development of nanostructured dielectric materials for various high energy, high power density electrical applications. It is demonstrated that novel electrical/dielectric properties can be achieved via the nanostructure and interface engineering. We present a high level summary of the progress achieved as well as challenges remaining in nanostructural engineering towards high energy density capacitor for energy storage and conversion, high voltage varistor for surge suppression and high proton conductivity membrane for fuel cell applications.

Tunable Nanodielectric Composites

This paper presents a progress update with the development of nanodielectric composites with electric field tunability for various high energy, high power electrical applications. It is demonstrated that nonlinear electrical/dielectric properties can be achieved via the nanostructure and interface engineering. A high level summary was given on the progress achieved as well as challenges remaining in nanodielectric engineering towards high energy density capacitors for energy storage and conversion, nonlinear dielectrics for tunable device, and high voltage varistor for surge suppression.

Mechanical and Thermal Properties

In the past decade, significant progress has been made in the area of advanced polymer materials, especially polymer nanocomposites. Future technology trends demand higher performance and lightweight materials in order to meet system level operational and reliability requirements. By combining the specific properties of the polymer matrix and the unique properties of nano-sized particles, a broad spectrum of properties of nanocomposites can be realized. Optimum combinations of mechanical, electrical and thermal properties of polymer materials can be tuned using proper choices of nanoparticles, coatings and processing conditions. In this chapter, recent developments on improving the mechanical and thermal properties of polymer nanocomposites will be summarized.