Anisotropic thermal conductive properties of hot-pressed polystyrene/graphene composites in the through-plane and in-plane directions

The interactions between polystyrene (PS) and graphene as well as the factors leading to anisotropic thermal conductive properties in the in-plane and through-plane directions of the hot-pressed samples were studied. In this procedure, the PS/graphene composites (PG) were prepared via solution mixing followed by hot-pressing method, the graphene oxide (GO) was simultaneously modified and reduced to graphene nanosheets by p-phenylene diamine. And the polydispersity index of PS matrix was controlled at as narrow as 1.14 by reversible addition-fragmentation chain transfer (RAFT) polymerization. The characterization showed that the thermal conductivity of PG composites with 10 wt% graphene loading was enhanced by 66% to 0.244 W m−1 K−1 compared with 0.147 W m−1 K−1 of pure PS. The thermal diffusivity (α) of hot-pressed PG samples showed anisotropic behavior according to the heat transfer directions. The α of in-plane direction was almost ten times higher than that of in through-plane direction. And both of them changed slowly in function of graphene loadings. This anisotropic property may be caused by the ordered arrangement of graphene sheets and PS chains after PG composites were hot-pressed.