Graphene is a flat sheet of carbon atoms arranged in a honeycombed lattice. It has been attracting the attention of scientists and engineers alike since it was first created in 2004 by mechanical exfoliation of bulk graphite. The unique electronic and thermal properties of graphene could come in useful for making a host of novel electronics devices. These include transistors that are faster than any that exist today thanks to the fact that electrons move extremely fast in the carbon material.

Graphene by itself has a very high intrinsic thermal conductivity, in the 2000–5000 W/mK range near room temperature, which is greater than the thermal conductivity of diamond (the best bulk heat conductor known). Although the thermal conductivity of graphene does drop when it is placed on a substrate, it still remains relatively high. The thermal conductivity decreases because phonons – quantized vibrations of the crystal lattice that transport heat – couple across the different atomic layers in the carbon material and this phonon scattering disrupts heat conduction.

Balandin and Novoselov’s team looked at how graphene laminate films increased the thermal conductivity of polyethylene terephthalate (more commonly known as PET). The researchers used a non-contact optothermal Raman technique for the thermal measurements. In this technique, the micro-Raman spectrometer is used as a sort of thermometer to measure temperature increases of the sample, and the exciting laser employed in the apparatus is also used as a heater. Team member Hoda Malekpour, a PhD student in Balandin’s group, was responsible for making these measurements.

“Our results reveal that the thermal conductivity of PET increases by up to 600 times when it is coated with the graphene laminate films,” Balandin tells nanotechweb.org. “The thermal conductivity of PET on its own is very low – in the 0.15–0.24 W/mK range at room temperature – and other plastic materials are also poor conductors of heat. This drawback prevents plastics from being employed in many applications that could benefit from their low cost, durability and light weight. Our work proves that a few micron-thick graphene layer deposited on plastic films can drastically improve the way they conduct heat and so now make such applications possible.”

The team, which includes scientists from the University of California Riverside, the University of Manchester, Bluestone Global Tech in New York and Moldova State University, used a fairly simple theoretical model in this work to explain how the thermal conductivity of graphene laminates depends on graphene flake size and impurity concentrations. “We would now like to develop a more detailed model based on multiscale simulations of heat transport in graphene to optimize its use as a coating material in thermal management applications,” says Balandin.

The current research is detailed in Nano Letters.