Abstract
In this work, in-plane and through-plane thermal diffusivities and conductivities of a freestanding sheet of graphene nanoplatelets are determined using photothermal beam deflection spectrometry. Two experimental methods were employed in order to observe the effect of load pressures on the thermal diffusivity and conductivity of the materials. The in-plane thermal diffusivity was determined by the use of a slope method supported by a new theoretical model, whereas the through-plane thermal diffusivity was determined by a frequency scan method in which the obtained data were processed with a specifically developed least-squares data processing algorithm. On the basis of the determined values, the in-plane and through-plane thermal conductivities and their dependences on the values of thermal diffusivity were found. The results show a significant difference in the character of thermal parameter dependence between the two methods. In the case of the in-plane configuration of the experimental setup, the thermal conductivity decreases with the increase in thermal diffusivity, whereas with the through-plane variant, the thermal conductivity increases with an increase in thermal diffusivity for the whole range of the loading pressure used. This behavior is due to the dependence of heat propagation on changes introduced in the graphene nano-platelets structure by compression.
Highlights
Graphene is a 2D layer of carbon atoms arranged in hexagonal rings
The in-plane thermal diffusivity was determined by the use of a slope method supported by a new theoretical model, whereas the through-plane thermal diffusivity was determined by a frequency scan method in which the obtained data were processed with a developed least-squares data processing algorithm
These changes are detected by a probe laser beam (PB) skimming the sample surface, suffering a deflection that causes phase and amplitude changes related to the beam position changes at the detector
Summary
Graphene is a 2D layer of carbon atoms arranged in hexagonal rings. Currently, it attracts a growing research interest due to its unique properties, including structure (the theoretical value of the specific surface area is 2630 m2 g−1), rigidity (Young’s modulus is approximately 1100 GPa) and strength (the fracture strength is about 125 GPa). Photothermal beam deflection spectrometry (BDS) is nowadays widely used for materials characterization to determine their thermal, optical, elastic and related properties (structural, transport) [14,15,16,17] It is a non-contact and non-destructive technique that provides high spectral, spatial, and temporal resolution, as well as high sensitivity. The generation of TOs leads to the creation of a density gradient in the adjacent gas layer and a change in its index of refraction These changes are detected by a probe laser beam (PB) skimming the sample surface, suffering a deflection that causes phase and amplitude changes related to the beam position changes at the detector. The in-plane thermal diffusivities and conductivities of GNP samples were found by collecting the SPDt signal as a function of the distance between the EB and PB and performing the multiparameter fitting of curves obtained from Equation (14) to the experimental data
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