Polymer-disordered carbon black composites

Imaging and Electrical Resistivity Measurements of Disordered Carbon-Black-Polymer Composites... 

This chapter reviews some of the work done on disordered carbon-black-polymer composites by my collaborators and myself over the past several years. These composites have widespread commercial applications. A qualitative analysis of a transmission electron microscope image is presented. Quantitative analyses of scanning probe microscope images and dc electrical resistivity data are presented. The resistivity and linear expansion of a typical composite between 25 and 180 C are measured and analyzed. The scaling theory of percolation provides a good explanation of most of our data. 

Disordered carbon-black-polymer composites have many common uses in modem technology. These uses include inks, automobile tires, reinforced plastics, wire and cable sheaths, antistatic shielding, resettable fuses, and self-regulating heaters. As an immediate example, the inked letters on this page consist of a disordered carbon-black-polymer composite bound to the surface of the paper. Despite these widespread applications, many of the important physical properties of these composites are not well understood. There is a long history of experimental and theoretical work on disordered carbon-black-polymer composites [7]. One of the most exciting recent advances in the field has been the application of the scaling theory of percolation [2] to these composites. This is based on the many similarities between the percolative transition in a disordered conductor-insulator composite and the thermodynamic phase transition common in many materials. 

Scanning Probe Microscopy. The scanning probe microscope (SPM) is a commercially available instrument (Nanoscope III, from Digital Instruments) that offers a relatively new means to distinguish continuous conductive pathways in disordered carbon-black-polymer composites. Figure 2 is a schematic illustration of how the SPM can be used to image carbon-black-polymer composites. 

The electrical properties of disordered carbon-black-polymer composites are critical to many of their commercial applications. Many research groups have used scaling laws to explain the electrical resistivity of disordered conductor-insulator composites. Some results [P] appear to obey scaling laws with a critical exponent in good agreement with the theoretical three-dimensional percolation value [2] 2.0. Other... 

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