Percolation and Electrical Conductivity Modeling of Novel Microstructured Insulator-Conductor Nanocomposites Fabricated
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Percolation and Electrical Conductivity Modeling of Novel Microstructured Insulator-Conductor Nanocomposites Fabricated from PMMA and ATO Youngho Jin1 and Rosario A. Gerhardt1 1 School of Materials Science and Engineering, Georgia Institute of Technology Atlanta, GA 30332-0245, U.S.A. ABSTRACT The electrical conductivity of insulating polymer matrix composites undergoes radical increase at a certain concentration of conductive filler, which is known as the percolation threshold. Polymer matrix conductive nanocomposites were fabricated by compression molding the mechanically mixed poly (methyl methacrylate) (PMMA) and antimony tin oxide (ATO) nanoparticles, as has been done with other polymer composites before. The electrical conductivity of PMMA/ATO nanocomposites increased by several orders of magnitude at a small concentration of ATO (~ 0.27 vol %). The continuous 3D network like distribution of ATO nanoparticles contributed to this percolation at subcritical filler concentrations. The effects of processing parameters on these unique microstructures and electrical properties were investigated. The tetrakaidecahedron-like microstructure was observed by scanning electron microscopy (SEM) and was found to be affected by the molding pressure, temperature and amount of nanoparticles. The viscoelastic flow of matrix under the optimum processing conditions allowed the shape transformation of PMMA into space filling polyhedra and an ordered distribution of ATO nanoparticles along the sharp edges of the PMMA. Parametric finite element analysis was performed to model this unique microstructure-driven percolation. The 2D simplified model was generated in AC/DC frequency domain mode in COMSOL Multiphysics® to solve the effects of ordered distribution of conductive nanoparticles on the electrical properties of the composite. There was excellent agreement between experimental and simulated values of electrical conductivity and percolation concentration. This model can be used to predict percolation threshold and electrical properties for any types of composite systems containing insulating matrix and conductive fillers that can form this unique microstructure. INTRODUCTION Polymer matrix composites containing conductive fillers can have a large range of electrical properties, while retaining the original physical properties of the matrix polymer. PMMA matrix nanocomposites were fabricated using antimony tin oxide as the conductive filler. By creating an ordered segregated distribution of nanoparticles, the electrical conductivity increased by several orders of magnitude at a very low concentration of filler. This was possible by confining the filler particles to certain regions of the composite[1-4]. The advantage of this method is that the percolation threshold (pc) can be minimized to lower the cost, to make the processing simple and to produce multifunctional composites with balanced electrical conductivity, transparency and thermo mechanical stability. Since this method is highly dependent on the processing parameters rathe
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