By Josh Perry, Editor
[email protected]

A team of scientists at Chalmers University of Technology (Gothenburg, Sweden) have developed a graphene assembled film that demonstrates 60 percent higher thermal conductivity than graphite film, despite graphite being many layers of graphene.

Researchers showed a graphene assembled film that has higher thermal conductivity than graphite. (Wikimedia Commons)

According to a report from the university, single layer graphene has a thermal conductivity range of 3,500-5,000 W/mK, while graphite films, which are popular for cooling mobile and other devices, have a thermal conductivity of up to 1,950 W/mK.

Graphene assembled films had a thermal conductivity as high as 3,200 W/mK, 60% higher than graphite. It also showed three times higher mechanical tensile strength, reaching 70 MPa

To achieve this level of conductivity, researchers controlled the grain size and the stacking order of graphene layers.

“The high thermal conductivity is a result of large grain size, high flatness, and weak interlayer binding energy of the graphene layers,” the article explained. “With these important features, phonons, whose movement and vibration determine the thermal performance, can move faster in the graphene layers rather than interact between the layers, thereby leading to higher thermal conductivity.”

This manufacturing process will be controlled by SHT Smart High Tech AB, which is a spin-off from Chalmers seeking to commercialize the technology.

The research was recently published in Nano Micro Small. The abstract read:

“Due to substantial phonon scattering induced by various structural defects, the in?plane thermal conductivity (K) of graphene films (GFs) is still inferior to the commercial pyrolytic graphite sheet (PGS). Here, the problem is solved by engineering the structures of GFs in the aspects of grain size, film alignment, and thickness, and interlayer binding energy.

“The maximum K of GFs reaches to 3200 W m⁻¹ K⁻¹ and outperforms PGS by 60%. The superior K of GFs is strongly related to its large and intact grains, which are over four times larger than the best PGS. The large smooth features about 11 µm and good layer alignment of GFs also benefit on reducing phonon scattering induced by wrinkles/defects. In addition, the presence of substantial turbostratic?stacking graphene is found up to 37% in thin GFs.

“The lacking of order in turbostratic?stacking graphene leads to very weak interlayer binding energy, which can significantly decrease the phonon interfacial scattering. The GFs also demonstrate excellent flexibility and high tensile strength, which is about three times higher than PGS.

“Therefore, GFs with optimized structures and properties show great potentials in thermal management of form?factor?driven electronics and other high?power?driven systems.”