Severe graphene nanoplatelets aggregation as building block for the preparation of negative temperature coefficient and healable silicone rubber composites

With the request of higher performance in automotive products, sealing components and materials resisting to severe conditions, the performance requirements for silicones are becoming ever more diverse and sophisticated. In this article we prepared silicone rubber (SR)-graphene nanoplatelets (GNPs) composite via liquid mixing method; the mechanical strength of the GNPs estimated by applying quantized fracture mechanics suggested a severe GNPs agglomeration that was confirmed by scanning electron microscopy analysis. We observe that such SR/GNP composite behaves as a negative temperature coefficient material, exhibiting electrical resistance decrease with temperature increase. It was also shown how the damaged SR/GNP composite can be healed by simple thermal annealing. The healing mechanism was rationalized in terms of “living” reactive species that are not consumed by curing at room temperature and promote, when thermally activated, the crosslinking among the damaged network of oligomers. The healing efficiency, expressed as crack length vs. annealing temperature, has been estimated again applying the principles of quantized fracture mechanics. These results could satisfy many of the demanding requirements of the silicone rubber materials used in daily life and indicate that SR/GNP composites can act as healable and temperature sensor materials e. g. for seals, hoses and automotive sector.