Microstructure-Based Simulation of the Dielectric Properties of Polymer-Ceramic Composites for Capacitor Applications
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0949-C05-01
Microstructure-Based Simulation of the Dielectric Properties of Polymer-Ceramic Composites for Capacitor Applications Jeffrey P. Calame Code 6843, Naval Research Laboratory, 4555 Overlook AV SW, Washington, DC, 20375
ABSTRACT Research on the microstructure-based modeling of composite dielectrics for capacitor applications is described. Methods for predicting the composite dielectric permittivity and internal electric field distributions within the microstructure using finite difference quasielectrostatic modeling are described, along with methods of generating realistic model spaces of particulate microstructures. An existing algorithm for generating random, monosized spheres-ina-dielectric matrix model spaces is modified to allow the treatment of bimodal composites in which small particles are deliberately segregated into the spaces between large particles. Such composites can have substantially higher total volumetric filling fractions of particles, leading to higher composite permittivity. The variations in permittivity with the filling fractions of bimodal inclusions are studied with the new model, with cases covering three different types of polymer matrix material. The effect of the small particle additions on the electric field statistics within the polymer matrix is also explored. INTRODUCTION A critical issue in composite dielectrics is the prediction of the properties of the composite based on knowledge of the constituent properties and geometry. Specifically, given a detailed microstructure of the composite, one would like to be able to predict, using computer simulations, the real and imaginary parts of the dielectric permittivity (ε ′ −jε ′′) of the composite and the internal distribution of electric fields, without resorting to free parameters. The ultimate goal is the complete modeling of composite materials for capacitors at the microstructure level, including both mesoscale features (individual particles, ensembles of particles in a matrix) and the truly microscopic features (interfacial effects, coatings, local dipolar interactions in surface layers, etc.). Such a capability would allow experimental synthesis to be focused on the most promising microstructural approaches, without the need to physically test each idea. Within a specific class of microstructures, the computational capability would provide explicit guidance to synthesis efforts, for example allowing the intelligent selection of particle shapes, loading fractions, surface coatings, and hierarchical assembly strategies. Finally, the computational techniques will provide a means of understanding experimental results on existing and new materials.
In a previous publication, finite difference quasi-electrostatic modeling of simple composites, consisting of spherical ceramic particles of barium titanium oxide (BTO) in various polymer background matrices, was performed [1]. The polymer materials used in the simulations included a high-ε relaxor ferroelectric terpolymer, namely poly vinylidene fluoridetrifluoroethylene-chlorof
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