Electrical conductivity and dielectric properties of PMMA/expanded graphite composites

PMMA/expanded graphite (EG) composites were prepared by direct solution blending of PMMA with the expanded graphite filler. Electrical conductivity and dielectric properties of the composites were measured by a four-point probe resistivity determiner and a dielectric analyzer (DEA). Interestingly, only 1 wt.% filler content was required to reach the percolation threshold (phi) of transition in electrical conductivity from an insulator to a semiconductor using PMMA/EG. The thickness of the interlayer of the expanded graphite was shown to be close to the nanometer scale. The reported filler content was much lower than that required for conventional PMMA/carbon black (8 wt.% carbon) and PMMA/graphite (3.5 wt.% graphite) composites. The improvements in both electrical conductivity and structural integrity were attributed to the difference in filler geometry (aspect ratio and surface area) and the formation of conductive networks in the composites. (C) 2002 Elsevier Science Ltd. All rights reserved.