L. Prystaj, E.A. Lucas, K. Alston, R.A. Gerhardt
Georgia Institute of Technology, United States
pp. 149 - 152
Keywords: PMMA, carbon black, carbon nanotubes, percolation, electrical conductivity
Polymer composites can be used for applications such as electromagnetic shielding devices, self-regulating heaters, over temperature protection structures, temperature sensors, devices that can control and regulate the flow of electrical current as well as antistatic materials. For optimal performance in the application intended for the composite, an ideal interconnected filler network needs to be maintained. Common fillers used to study the properties and characteristics of polymer filled composites are carbon fibers, metallic powders and Carbon Blacks (CB) . Carbon blacks have been a desired filler type for many years due to their inexpensive cost and their wide availability in a variety of various particle sizes.. More recently, the work on polymer nanocomposites have been dominated by papers focusing on using single wall carbon nanotubes, multiwall carbon nanotubes, graphite nanoplatelets and graphene. However, many of these newer materials are quite expensive therefore it is desirable to find a way to obtain the needed electrical response at minimal cost, while maintaining the mechanical integrity of the wanted components. A method of producing a segregated microstructure has been developed that has led to a substantial decrease in the amount needed to achieve electrical percolation in these composites. A study investigating the effect of the microstructure on the percolation threshold was done using polymethyl methacrylate (PMMA)/ CB composites. The results of the extensive study showed that the percolation threshold for a random microstructure was 2.7 vol%CB and nanocomposites with a segregated microstructure, the percolation threshold decreased to 0.26 vol%CB.. The formation of a continuous network allows electrons to have a path to travel throughout the system and result in a dramatic decrease (several orders of magnitude) in the resistivity of the system. The percolation threshold is strongly influenced by the materials used and the processing method utilized to make the composite. Not only does the fabrication method used influence the percolation threshold, but the characteristics of the fillers used can also play a role. In this paper, we will present results on a series of composites made by the same exact method but utilizing carbon blacks with different characteristics such as their size and surface area and compare their behavior to composites made with short multiwall carbon nanotubes which have been extensively characterized as free-standing films. It is shown that the individual characteristics of the different fillers have an effect on the details of the percolation region as shown in Figure 1 and can be more clearly studied using frequency dependent measurements known as impedance spectroscopy.