Impedance spectroscopy and optical characterization of polymethyl methacrylate/indium tin oxide nanocomposites with three-dimensional Voronoi microstructures

Abstract

This study describes the optical and ac electrical characterization of polymethyl methacrylate (PMMA)/indium tin oxide (ITO) nanocomposites containing a Voronoi-type segregated network microstructure. Optical transmission microscopy, scanning electron microscopy (SEM), and impedance spectroscopy were used to investigate the microstructure and electrical properties of the composites. The complex refractive index values of the composites were measured by using a modified version of the internal reflection intensity analysis (IRIA) method. SEM images of the composites reveal that the microstructure consists of polyhedral-shaped PMMA particles, where the ITO nanoparticles become concentrated along the edges of the PMMA to form a percolated network. Electrical measurements as a function of filler content indicate that the percolation threshold is <0.50 vol % ITO. The in-plane and through-plane refractive indices obtained by the modified IRIA method suggest that the microstructure is isotropic. The estimated extinction coefficients increase with higher ITO content, which is expected for a percolating system. A microstructural model, which takes into account the accumulation of the ITO nanoparticles at the edges of the polyhedron-shaped PMMA particles, is proposed that can predict the percolation threshold in composites that have Voronoi-type segregated network microstructures.