Broadband dielectric spectroscopy of multilayer graphene/epoxy nanocomposites

Graphene is a carbon-based allotrope material which, since very few years, appears as very exciting due to incredible physical properties such as a high electron mobility (250,000 cm²/Vs), a high thermal conductivity (5,000 W/mK) and a high Young´s modulus (1 TPa). Obtained from the exfoliation of graphite pristine in the form of multilayer graphene (MLG) nanoplatelets, it focuses an increasing attention when mixed to a polymer matrix to produce MLG/polymer nanocomposites. Up to now, few studies have mainly reported on the effects on the thermal conductivity of various MLG/polymer nanocomposites. However, no study has been led on their dielectric properties. In this paper, we propose to study the impact of MLG on the dielectric permittivity and losses of an epoxy nanocomposite with different low nanoflakes filler contents from 0.005 to 0.5 wt.%, chosen below the electrical percolation threshold. The study will be performed both in wide temperature and frequency ranges in order to highlight the influence of the MLG nanoplatelets on the epoxy relaxation dynamics using a broadband dielectric spectrometer from Novocontrol. The MLG loading causes an increase of the polarizability of the composite material and thus the dielectric losses. At high temperature, at small MLG additions, the graphene particles interfere with the cooperative movements associated with the vitreous transition temperature, increasing the permittivity and decreasing the losses.