Edge and basal functionalized graphene oxide nanosheets: Two different behavior in improving electrical conductivity of epoxy nanocomposite coatings

Abstract

Two different graphene nanosheets with different oxygen groups' localization were synthesized to investigate their effect on the electrical properties of graphene/epoxy nanocomposite coatings. Graphite natural flakes (NG) and expanded graphite (EG) were used as a carbon precursor to synthesize Edge functionalized (E-GO) and Basal Functionalized (B-GO) graphene nanosheets, respectively. Next, polymer nanocomposite coatings were fabricated by dispersing E-GO and B-GO into a waterborne epoxy matrix. Rheology was assisted in evaluating the dispersion state of the nanosheets in the epoxy matrix. B-GO exhibited better performance in network formation which can be related to the similarity of oxygen groups between B-GO and epoxy matrix. Next, the electrical conductivitie values of polymer nanocomposite coatings were measured after in-situ thermal reduction at 225 °C. The results indicated that polymeric coatings containing B-GO nanosheets represent higher electrical conductivity values compared to samples containing E-GO nanosheets despite the higher intrinsic electrical conductivity of E-GO compared to B-GO. This can be related to the improved ability of B-GO nanosheets to form an electrically conductive network inside the epoxy matrix. The electrical conductivity value of 0.5 S/m was obtained for polymeric coatings containing 0.8 vol% B-GO nanosheets with percolation thresholds of 0.17 vol%. The improved electrical conductivity can be correlated to the formation of the interphase region between the epoxy matrix and B-GO nanosheets which is the result of the similarity of the oxygen groups' nature in B-GO and epoxy.