Non-linear conductivity dependence on temperature in graphene-based polymer nanocomposite

The temperature dependence of electrical conductivity of nanocomposites with polystyrene and graphene platelets (GNPs) was studied. It was found that for low loadings of GNPs the conductivity behaviour changed significantly within the temperature range of 295–369 K. Thus, conductivity saw a drop with decrease of temperature from 369 to 331 K. The corresponding curve was approximated by the mechanism of hopping conductivity. Within the temperature range of 331–305 K a slight decrease of conductivity was observed. The latter was well-fitted by exponential curve with coefficients related to fluctuation-induced tunnelling of electrons between neighbour graphene platelets. Within the low-temperature range of 305–295 K a growth of conductivity was explained by increasing of electron tunnelling through the contact caused by the creation of electret state. The latter was presumably formed by polarisation of the polymer between edges of two neighbouring graphene platelets. The observed dependence of conductivity upon temperature is non-linear for low loadings of GNPs and it is close to the linear dependence for higher loadings of the filler.