High aspect ratio graphene nanosheets cause a very low percolation threshold for polymer nanocomposites

Liquid exfoliated, high aspect ratio (1272) graphene nanosheets (GNS) are dispersed in thermoplastic polyurethane (TPU) to prepare range of nanocomposites. A three fold increase in direct current conductivity is recorded at 0.0055 volume fraction (V_{f}) of GNS-TPU composites as compared to pristine TPU. It is suggested that the percolation threshold for conducting network achieved at low filler loadings is due to the high aspect ratio and homogeneous dispersion of GNS within the polymer. The experimental results are interpreted using interparticle distance model and modified power law. The two models predict threshold filler loading in 0.015-0.001 range volume fraction GNS based on the average values of mean length and no. of layers per nanosheet. The experimental results favor modified power law as it relies on aspect ratio of fillers. A slight deviation in our study from modified power law may be due to aggregation in as prepared GNS.