Current conduction mechanisms in structural resins loaded with non-covalently functionalized graphene nanosheets

This work focuses on a non-covalent π-π interaction between graphene nanosheets (G) and a pyrenebased molecule (py). The proposed modification proved successful in preserving the relevant electronic properties of graphene, while promoting a better dispersion of the nanofiller due to the reduced viscosity with consequent improvement of the rheological properties of the formulated nanocomposites. Tunneling Atomic Force Microscopy (TUNA) analysis was carried out using Gpy weight percentages both below (0.1wt% of G-py) and above (1wt% of G-py) the Electrical Percolation Threshold (EPT) to investigate the current conduction mechanisms of the epoxy/graphene systems. In particular, for the lowest G-py load, in most of the sample domains, no electrically conductive paths are observed, while, for the highest G-py load, the presence of a conductive network at the nanoscale level with efficient adhesion to the interface indicates that the sample is above the EPT. The possibility to detect low currents also for the sample at the lowest G-py amount (0.1wt%) confirms the good electrical performance of the nanocomposites and, consequently, the successful performed functionalization. The electrical results are in perfect agreement with the rheological ones. In fact, the inclusion of a functionalized G-py amount of 0.5wt% caused the decrease in the complex viscosity of the unfilled epoxy resin, while instead, the same quantity of unfunctionalized G resulted in an increase of its viscosity. The non-covalent modification significantly improves the thermal stability of the graphene nanosheets, also determining an increase in the oxidative thermostability of the structural nanocomposites.