Detection of percolating paths in polyhedral segregated network composites using electrostatic force microscopy and conductive atomic force microscopy

2020

Mater. Res. Express

The objective of this study was to determine the effect of processing on the electrical properties and microstructure of MWCNTs/PMMA nanocomposites made by compression molding. Three different mixing methods were used: mechanical, solution, and melt mixing of the same starting materials. The composite microstructures were found to be segregated, agglomerated, and randomly distributed respectively. Electrical property measurements indicate that the mechanically mixed composites have the lowest percolation threshold of 0.05 phr (0.028 vol% MWCNT). Melt mixed composites have the highest percolation threshold of 4 phr (2.161 vol% MWCNT) while solution mixed composites have a percolation threshold of 2 phr (1.102 vol% MWCNT). These results indicate that the segregated microstructure allows for the CNTs to form a percolated network through the composite more easily than the other two methods. Fitted equivalent circuits to the measured impedance spectra show that after percolation the CNTs dominate the electrical properties as represented by an increase in the number of inductance circuit elements. Before or at percolation, the presence of PMMA plays a stronger role in the circuit. This article is novel in that this is the first study where direct comparison of the properties and microstructure of composites fabricated utilizing three different mixing methods using the same source materials can be made.

Section: Introductionmentioning

confidence: 99%

Effect of processing on the properties and morphology of MWCNT-polymer networks

Watt

2020

Mater. Res. Express

“…In previous studies in the Gerhardt group, it has been shown that compression molding of thermoplastic polymers will deform the particles into polyhedra, resulting in a dense, grain-like microstructure. 4,6 Under certain processing conditions, it was found that when compression molding mixtures of micrometer-scale insulating polymer particles and nanoscale conducting fillers, the polymer particles would have both a low enough viscosity to deform to make a dense structure and a high enough viscosity that the filler would not incorporate into the polymer particles. 4,7 This forced the filler particles into the boundaries between the polyhedra, resulting in the formation of a segregated network of the filler.…”

Section: Introductionmentioning

confidence: 99%

Comparison of hot pressing and spark plasma sintering in the densification behavior of indium tin oxide‐borosilicate glass composites

Rudzik

2017

J Am Ceram Soc

The goal of this study was to fabricate borosilicate glass matrix composites with high optical transmittance and high conductivity by forming percolated segregated networks of indium tin oxide (ITO) in the microstructure. ITO nanoparticles and borosilicate glass microspheres were mechanically mixed with ITO concentrations varying from 0 to 2.99 vol%. The mixes were then consolidated using either hot pressing (HP) or spark plasma sintering (SPS). The effects of changing sintering methods, along with varying other processing parameters such as heating rate, maximum temperature, and applied pressure, had surprising and unanticipated effects. Ac impedance spectroscopy (IS), SEM, and EDS results indicated the successful formation of a grain‐like microstructure of the sintered glass using both HP and SPS processing, with the ITO particles segregated to the boundary regions in all samples. IS results indicated percolation threshold values between 0.154 and 0.307 vol% ITO in the HP samples and between 0.307 and 0.764 vol% ITO in the SPS samples, with resistivities as low as 29 (Ω·cm) at 2.99 vol% ITO. Optical properties were dominated by impurities and light scattering at defects such as pores. Contrary to conventional belief, it was found that samples made using SPS required far higher temperatures to fully densify, with all other processing conditions being the same, compared with HP. This behavior was confirmed through repeat tests using different SPS equipment and a wide range of processing conditions.

“…From Figure 4, it can be seen that the biggest drop in resistivity occurs right after 0.1 phr, so this composition would give a great deal of information about the microstructure and what may be preventing percolation from occurring. Based on previous simulations and models, percolation should have occurred at lower compositions than 0.1 phr for this particle size [11]. Please note that the slightly lower resistivity data for the 0.001 phr sample is affected by carbon contamination from the hot press die and does not represent percolation, that is why a dashed line has been added.…”

Section: Shown Inmentioning

confidence: 93%

Fabrication of Conductive Glass Nanocomposites with Networks of Antimony Tin Oxide

Pruyn

2013

MRS Proc.

The percolation threshold in a ceramic composite depends on the processing conditions used to fabricate them along with the size and shape of the filler. In this study, borosilicate glass microspheres were used as the matrix material and nanosized antimony tin oxide (ATO) particles were used as the filler. The microsphere/ATO composites were fabricated by hot pressing around the glass transition temperature in order to control the viscosity. The pressure and temperature applied allowed the ATO to be confined to the spaces between certain glass particles, forming percolating networks at low volume fractions of the ATO. The electrical properties were examined using ac impedance spectroscopy. The impedance, electric modulus, and tan were studied which allowed for valuable insights in structure-property-processing relationships in these materials, along with determination of the percolation behavior in these composites. This analysis on samples right before percolation indicated that there was a highly resistive component affecting long range conductivity which is likely due to porosity at the triple points while the dielectric response is affected by the clusters of ATO nanoparticles. Based on this, the percolation of ATO should reduce down to lower concentrations if the processing conditions are improved to reduce this porosity and further segregate the ATO.