Transport behavior of PMMA/expanded graphite nanocomposites

Polymethylmethacrylate (PMMA)/expanded graphite (EG) and PMMA/untreated graphite (UG) composites were prepared by direct solution blending of PMMA with EG and UG fillers. A four-point resistivity probe system was used to measure the electrical conductivity of the composites. With the increase of filler content, the electrical conductivity of the composites showed the transition from an insulator to a semiconductor. The transition can be described by classic percolation theory with a critical exponent of 2.1 +/- 0.1 for PMMA/EG and 1.8 +/- 0.1 for PMMA/UG composites. Interestingly, only 0.6 vol% filler content was required to reach the percolation threshold of transition in electrical conductivity using PMMA/EG. The thickness of the EG sheet was found to be at the nanometer scale. The filler content necessary to reach the percolation threshold in PMMA/EG was found to be much lower than those required for PMMA/UG (2.0 vol% graphite) and conventional PMMA/carbon black (4.5 vol% CB) composites. Evidence was presented in this to demonstrate the improvement in electrical conductivity which was effected by the increase in filler form factor and their enhanced dispersion. (C) 2002 Elsevier Science Ltd. All rights reserved.