  Development of the next generation thermal interface materials with high
thermal conductivity is important for thermal management and packaging of
electronic devices. We report on the synthesis and thermal conductivity
measurements of non-curing thermal paste, i.e. grease, based on mineral oil
with the mixture of graphene and few-layer graphene flakes as the fillers. It
was found that graphene thermal paste exhibits a distinctive thermal
percolation threshold with the thermal conductivity revealing a sublinear
dependence on the filler loading. This behavior contrasts with the thermal
conductivity of curing graphene thermal interface materials, based on epoxy,
where super-linear dependence on the filler loading is observed. The
performance of graphene thermal paste was benchmarked against top-of-the-line
commercial thermal pastes. The obtained results show that non-curing graphene
thermal interface materials outperforms the best commercial pastes in terms of
thermal conductivity, at substantially lower filler concentration of ~ 27 vol%.
The obtained results shed light on thermal percolation mechanism in non-curing
polymeric matrices laden with quasi-two-dimensional fillers. Considering recent
progress in graphene production via liquid phase exfoliation and oxide
reduction, we argue that our results open a pathway for large-scale industrial
application of graphene in thermal management of electronics.
