Correlation of the ac Electrical Conductivity and the Microstructure of PMMA/ITO Nanocomposites That Possess Phase-Segregated Microstructures

Abstract

This paper investigates the effect of processing parameters on the microstructure and the ac electrical conductivity of poly(methyl methacrylate) (PMMA)/indium tin oxide (ITO) nanocomposites. The PMMA/ITO composites were fabricated by hot pressing ITO-coated PMMA powders and confining the ITO nanoparticles to the perimeter of the polymer phase. Correlations between the microstructure and the measured ac conductivity were determined by comparing scanning electron microscopy (SEM) images of fractured cross sections of the composites and the ac conductivity determined from impedance spectroscopy measurements. It was found that the microstructure of the PMMA/ITO composites consists of polyhedral-shaped matrix particles, which are affected by the starting amount of powder and compaction pressure used to form the composites. The critical frequency fc , which determines the transition from frequency-independent to frequency-dependent ac conductivity, was observed to increase as the steady state conductivity increased. When higher compaction pressures were used, the specimens had lower conductivities and the fractured surfaces showed deformed polyhedral shapes with combinations of rough and smooth regions. These changes in the microstructure of the composites were easily detected by the ac electrical conductivity measurements. The SEM images of the fractured cross-sections indicated that these changes in the ac conductivity were related to the local concentration of the ITO nanoparticles in the PMMA matrix. This study demonstrates that impedance spectroscopy is an excellent tool for examining structure−property relationships in polymer−matrix composites that possess phase-segregated microstructures.

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

“…The PMMA and ATO particles were mechanically blended for 10 min in a blender at room temperature as has been described in our previous papers. 1,8 The surface of the polymer matrix was uniformly covered by the ATO nanoparticles (NPs) during mechanical blending. However, localized heating in the blender should be avoided, because partial melting of the polymer spheres can decrease the connectivity of the filler-chain network during compression molding.…”

“…[1][2][3] Many processing techniques such as melt blending, 4 solution blending, 4,5 in-situ polymerization, 6 latex blending 7 and mechanical blending 1,8,9 have been used to fabricate polymer matrix conductive composites.…”

“…obtaining electrical percolation at low concentration of fillers. 1,8,9 The final electrical conductivity can be a Electronic mail: rosario.gerhardt@mse.gatech.edu. tunable by using fillers with different electrical conductivity, because this fabrication method provides ordered phase segregated filler networks, regardless of filler types.…”

“…13,14 The electrical properties and the percolation threshold can also be affected by the processing parameters, such as the mixing method used, the processing pressure and the temperature. Although the effects of the processing conditions on the electrical properties of conductive PMCs have been previously reported, 8,15 the influence of processing conditions have not yet been fully investigated or optimized yet. It is still difficult to determine under what conditions, the best properties can be obtained due to the fact that the combined effect of temperature, pressure, thickness and filler content provide a complex problem that requires detailed studies of a specific series of specimens to clarify.…”

“…The applied pressure can allow the polymer to flow into the capillaries between the filler particles and break up the network. 8 For the same reasons, compression molding temperature will also affect the electrical conductivity of the composites because the high processing temperature lowers the melt viscosity of the polymer during processing. 5,17 This paper focuses on the effects of the processing parameters including temperature, pressure, and sample thickness on the electrical conductivity of phase segregated polymer matrix composites made from polymethylmethacrylate (PMMA) and antimony tin oxide (ATO).…”