Conductive composites consist of a thermoplastic or thermosetting polymer matrix with an electrically conducting filler. The concentration of the electrically conducting filler must be above a critical value, called the percolation threshold, in order for the material to conduct electricity. These types of materials are used in many applications, because these materials combine electrical conductivity with the ability to be formed into complex shapes. If you've ever purchased a circuit board, it might have come shipped in a clear, darkened plastic; this plastic is almost certainly polyethylene filled with carbon black and protects the circuit board from damaging static electricity.
Our research is concerned with different facets of these materials. One project investigated how the presence of a conductive filler modified the crystallization kinetics of the polyethylene host. Crystallization is the phenomena where the polymer molecule forms an ordered array, think of taking all your cooked spaghetti on your plate and lining it up so that it all faces the same directions (the spaghetti has to fold like a horseshoe in order for the picture to be accurate). We found that the filler modifies the crystallization kinetics dramatically, and attributed this effect to the high thermal conductivity of the filler (we used nickel filler).
Another component of our work is to increase or control the conductivity of the composite by forming a conductive film right on the surface of the filler. We are not sure exactly how this conductive film changes the conductivity of the composite, but we have lots of theories. This method will increase conductivity orders of magnitude versus the same composite made with filler that hasn't been coated. We are currently wondering whether if films of different thicknesses will give different changes in conductivity. I'll keep you posted!!!!
W.B. Genetti, W.L. Yuan, B.P. Grady, E.A. O'Rear, C.L. Lai and D.T. Glatzhofer, "Polymer Matrix Composites: Conductivity Enhancement through Polypyrrole Coating of Nickel Flake", Journal of Material Science, 33, 3085 (1998)
W.B. Genetti, P.M. Hunt, M. Shah, A.M. Lowe, E.A. O'Rear and B.P. Grady, "Conductivity Enhancement of Polymer Composites through Admicellar Polymerization of Pyrrole on Particulate Surfaces", Fundamental and Applied Aspects of Chemically Modified Surfaces, J.P. Blitz and C.B. Little eds, (Cambridge, UK: Royal Society of Chemistry) 1999.
B.P. Grady, W. B. Genetti, R. J. Lamirand and M. Shah, "An Investigation of Heat Transfer Effects in Isothermal Crystallization Studies of Low-Density Polyethylene", Polymer Engineering and Science, 41, 820 (2001).
P. Lekpittaya, N. Yanumet, B.P.Grady, and E.A. O’Rear, “Resistivity of Conductive Polymer-Coated Fabric”, Journal of Applied Polymer Science, 92, 2629 (2004).