Comparison of the Electrical Properties of PS-PMMA-MWNT Composites Made by Three Different Fabrication Methods
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Comparison of the Electrical Properties of PS-PMMA-MWNT Composites Made by Three Different Fabrication Methods Samual J. Wilson2 and Rosario A. Gerhardt1,* 1
School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA, United States. 2
School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA, United States. *contact e-mail: [email protected] Abstract Polystyrene (PS), polymethyl-methacrylate (PMMA) and multi-walled carbon nanotubes (MWNT) were used to fabricate conductive nanocomposites using various mixing methods, followed by compression molding to analyze their electrical properties. The main objective of this research project was to evaluate how using different mixing techniques alter the composite microstructure and hence the properties of the resultant composite material. Three fabrication techniques were selected to be investigated: mechanical mixing, melt-mixing, and solution mixing. The concentration of the fillers was kept constant at 2 wt% MWNT to simplify comparisons. After mixing, the composite mixtures were compression molded at the same temperature of 180°C. It was found that each mixing method yielded uniquely different AC conductivity profiles which can be attributed to how the fabrication method used affected the arrangement of the CNTs in the composite structure. This newfound control of the electrical properties of the composite materials could definitely be useful to researchers because one can choose the proper fabrication technique based on what properties are desired. Introduction MWNTs have been researched extensively due to their unique electrical and mechanical properties.1 MWNTs can be used in a wide variety of applications such as nanoscale electronic devices, field effect transistors, and chemical sensors as free standing wires or as networks. Another commonly investigated application is to utilize CNTs as the conductive filler in polymer composites. Polymer matrix composites (PMCs), whether as films or bulk materials, generally have random microstructures where the filler is homogeneously dispersed. However, it has been demonstrated that segregation of the filler, by creating regions of excluded volume, allows the achievement of percolation at much lower contents of the filler2-4 than when they are homogeneously distributed. PMCs are often studied to determine how the concentration of the filler affects the mechanical or electrical properties of the bulk composite material.2-4 There are many studies that show that the properties of conducting PMCs can vary widely as a function of the concentration of MWNTs used.5-10 However, some of these are made with a single polymer while others are conducted using blends or copolymers. Previous researchers have also shown that using two immiscible polymers may allow for more options in fabrication that may yield different microstructures and different conductivity data.6,11 Furthermore, it has also been reported that
the microstructure of the PMCs produced during t
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