Abstract
The present work deals with the measurement of thermo-physical properties of a freestanding sheet of graphene (thermal diffusivity and thermal conductivity), and their dependence on sample density as result of uniform mechanical compression. Thermal diffusivity of graphene nano-platelets (thin slabs) was measured by the pulse flash method. Obtained response data were processed with a specifically developed least square data processing algorithm. GNP specific heat was assumed from literature and thermal conductivity derived from thermal diffusivity, specific heat and density. Obtained results show a significant difference with respect to other porous media: the thermal diffusivity decreases as the density increases, while thermal conductivity increases for low and high densities, and remain fairly constant for the intermediate range. This can be explained by the very high thermal conductivity values reached by the nano-layers of graphene and the peculiar arrangement of platelets during the compression applied to the samples to get the desired density. Due to very high thermal conductivity of graphene layers, the obtained results show that thermal conductivity of conglomerates increases when there is an air reduction due to compression, and consequent density increases, with the number of contact points between platelets also increased. In the intermediate range (250 ≤ ρ ≤ 700 kg·m-3) the folding of platelets reduces density, without increasing the contact points of platelets, so thermal conductivity can slightly decrease.
Highlights
Graphene, since its discovery,[1] has attracted a growing attention in the scientific community due to its exceptional properties
When a single-layer graphene is supported on an amorphous material, the thermal conductivity is reduced to about 500÷600 W·m1·K1 at room temperature as a result of scattering of graphene lattice waves by the substrate,[5,6] and can be even lower for few graphene layers encased in amorphous oxide.[7]
Flash method is widely used for evaluating thermal diffusivity (α) of various materials
Summary
Since its discovery,[1] has attracted a growing attention in the scientific community due to its exceptional properties. The material under investigation are graphene nano-platelets in a form of free standing low density conglomerate. Taking into account the multiple possible applications of this material, the knowledge of its properties is fundamental to predict its behaviour in practical uses. Between these properties thermal and thermophysical ones take a great importance due to their effect in many applications in heat conductors or heat storage systems. The present work deals with measurement of thermo-physical properties of freestanding sheets of graphene nano-platelets (thermal diffusivity and thermal conductivity), and their dependence on the density of the samples
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