Significantly reduced c-axis thermal diffusivity of graphene-based papers

Owing to their very high thermal conductivity as well as large surface-to-volume ratio, graphene-based films/papers have been proposed as promising candidates of lightweight thermal interface materials and lateral heat spreaders. In this work, we study the cross-plane (c-axis) thermal conductivity (k _c ) and diffusivity (α _c ) of two typical graphene-based papers, which are partially reduced graphene paper (PRGP) and graphene oxide paper (GOP), and compare their thermal properties with highly-reduced graphene paper and graphite. The determined α _c of PRGP varies from (1.02 ± 0.09) × 10^-7 m² s^-1 at 295 K to (2.31 ± 0.18) × 10^-7 m² s^-1 at 12 K. This low α _c is mainly attributed to the strong phonon scattering at the grain boundaries and defect centers due to the small grain sizes and high-level defects. For GOP, α _c varies from (1.52 ± 0.05) × 10^-7 m² s^-1 at 295 K to (2.28 ± 0.08) × 10^-7 m² s^-1 at 12.5 K. The cross-plane thermal transport of GOP is attributed to the high density of functional groups between carbon layers which provide weak thermal transport tunnels across the layers in the absence of direct energy coupling among layers. This work sheds light on the understanding and optimizing of nanostructure of graphene-based paper-like materials for desired thermal performance.