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.

Fabrication and simulation of semi-transparent and flexible PMMA/ATO conductive nanocomposites obtained by compression molding at different temperatures and pressures

“…[22][23][24] During this shape transformation, ATO NPs were primarily forced to be aligned along the edges to form percolation networks, while quite a number of ATO NPs still occupied the interfaces. In the composites with the filler content slightly below the percolation threshold (Figs.…”

Thermal effects on the percolation behavior of polyvinylidene fluoride/nickel composites

“…Still a lot of controversy exists which requires serious attention. Previous reports in literature showed that the value of P C depends on various parameters, such as, size, shape, spatial distribution, adhesiveness, viscosity, wetting of the polymer, polymer matrix, process conditions, etc 1–8, 11–26. This has motivated us to consider a systematic study to optimize P C as a function of various parameters, such as, materials processing conditions, shape and size of the fillings, rheological properties of the matrix, etc.…”

“…(1) to the conductivity data for 0.40 sample shows that the value of n was found to be 0.78 which is well within the Johnscher's universal value of between 0 and 1 36. The frequency which separates the region of ac and dc conductivity region is called critical frequency or hopping frequency ( f c ) 25. The critical frequency is normally determined by locating the intersection of the lines that are tangent to the frequency‐dependent and frequency‐independent regions.…”

“…The various conductive fillers, such as, metal fillers,4–8, 11–13 carbon fibers,1, 14–17 conductive carbon black,2, 3, 18–22 graphite nanoplates,23, 24 and other types of conductors25, 26 have been used in practice. These composites are of recent interest because of their high dielectric constant, easy processing, flexibility, ability to absorb mechanical shock, etc 1–26. It is well‐known that these random insulator/conductor composites (ICC) undergo a metal–insulator transition (MIT) at a critical concentration of the metal (conductor) in the composite.…”

“…It is well‐known that these random insulator/conductor composites (ICC) undergo a metal–insulator transition (MIT) at a critical concentration of the metal (conductor) in the composite. The percolation theories (for these random continuum percolation systems27, 28) predict the ideal percolation threshold ( P C ) i.e., the critical volume fraction for any 3D random percolative ICC to be at 0.1629–31 (where the fillers are assumed to be of hard spheres), where as experimentally the P C value is found to be at variance 1–8, 11, 12, 14–26. The focus of research in polymer/conductor composites is on P C and the critical behavior in the vicinity of MIT.…”