An international team of scientists has found the thermal conductivity of graphene changes depending on the size of the material sample, a discovery they say challenges the fundamental laws of heat conduction for extended materials.
Davide Donadio, head of a research group at the Max Planck Institute for Polymer Research (MPI-P) in Germany and his colleagues from the National University of Singapore predicted this phenomenon using computer simulations and verified it with experiments. Their research is published in the scientific journal Nature Communications.
“We recognized mechanisms of heat transfer that actually contradict Fourier’s law in the micrometer scale. Now all the previous experimental measurements of the thermal conductivity of graphene need to be reinterpreted. The very concept of thermal conductivity as an intrinsic property does not hold for graphene, at least for patches as large as several micrometers,” Donadio said.
The discovery disputes Fourier’s law, which describes the laws of heat propagation in solids. Accordingly, thermal conductivity is an intrinsic material property that is normally independent of size or shape. In graphene, however, this is not the case.
Using experiments and computer simulations, the MPI-P-NUS team found that the thermal conductivity of graphene logarithmically increases as a function of the size of the samples—that is, the longer the graphene segment, the more heat can be transferred per length unit. The researchers believe this feature stems from “the combination of reduced dimensionality and stiff chemical bonding, which make thermal vibration propagate with minimal dissipation at non-equilibrium conditions.”
The new research complements other characteristics exhibited by the wonder material, including high electrical conductivity, chemical stability and mechanical strength. Graphene was also already known to be an excellent heat conductor, albeit its thermal conductivity was regarded as a material constant.
With this new characteristic, graphene could be particularly useful in micro- and nano-electronics applications, where heat is a limiting factor for smaller and more efficient components.
