Enhancing the electrical conductivity of polymer composites

An effective approach to reduce inter-particle gaps by nanofillers for making highly conductive polymer composites was reported based on the conductive tunnelling mechanism. A low percentage of nanosized conductive carbon filler (carbon black and graphite) or ions (Li+, Na+ and K+) was filled into the tunnelling phase of expanded graphite (EG) sheets, by which electron transport was enhanced across the junctions of EG sheets and a significant increase in the electrical conductivity of the composites was achieved. In this report, polyethylene (PE) and polyethersulphone (PES) were selected as model materials. The results indicated that for the EG/PE composite the conductive peculation threshold was less than 2 wt% and its conductivity increased three orders of magnitude with the addition of only 1 wt% nanofiller compared with the EG/PE composite. By introducing a very small amount of Li+ or Na+ (0.06 wt% related to EG) the electrical conductivity was further enhanced by two orders of magnitude compared to the EG/PES composite. Experimental results were well understood by the theoretical study of the electron transport behaviour in the EG/polymer composites. The gaps between graphite sheets in the matrix must be no larger than 10 nm if the EG/PE composite is to become electrically conductive.