▎ 摘　　要

Results of broadband dielectric spectroscopy of epoxy resin composites containing graphene nano platelets (GNP) are presented in a wide temperature range (25-500 K). The as-produced composites were heated at temperatures above the epoxy glass transition and subsequently cooled down to room temperature. This annealing was proved to be a simple but powerful process to improve significantly the electromagnetic properties of the GNP-based composites. The dc conductivity of epoxy filled with 4 wt% GNP is 68 times higher after annealing. Another benefit of the annealing is to lower substantially the percolation threshold, from 2.3 wt% for as-produced samples to 1.4 wt%. In composites above the percolation threshold, the electrical conductivity is the result of tunneling between GNP clusters. For a given GNP concentration, the tunnel barrier decreases after annealing. (C) 2016 Elsevier Ltd. All rights reserved.