Nov 16, 2010
Tuning particle size of graphite nanoplatelets for improved thermal management
Increasing packaging density in modern electronics requires more efficient thermal interface materials (TIMs) for improved thermal management. Particle-laden polymers dominate the market for commercial TIMs with particles of nanoscale dimensions such as Al2O3, BN, Al and Ag providing state-of-the-art heat transfer performance.
Recently, graphite nanoplatelets (GNPs), which are comprised of a few graphene layers, have been shown to demonstrate superior enhancement to the thermal conductivity of the polymer matrix because of their high intrinsic thermal conductivity and high aspect ratio.
In this study the authors showed that the choice of the starting natural graphite (NG) material is a crucial factor in the synthesis of high performance GNP fillers for TIMs. The optimum lateral particle size of natural graphite particles for the production of high aspect ratio GNPs is in the range of 200–400 µm; for natural graphite of smaller or larger particle size the exfoliation is incomplete and the thermal performance of the resulting GNP filler is reduced.
A detailed statistical study of laboratory scale and commercial GNP materials showed a surprisingly wide distribution of lateral particle sizes, from submicron to 50 µm in lateral dimensions: the smaller particles (<5 µm) dominate the total particle count (98%) while the larger particles (>5 µm) dominate the volume and mass (>80%) of the bulk GNP sample.
Thus the conventional perception of GNP material as particles of few nanometres in thickness and of submicron or micron lateral size needs to be revisited in most practical applications. In thin thermal interface layers the larger GNP particles are probably forced to orient in the plane of the thermal interface layer and the direction of the required heat dissipation will be oriented in the direction of low thermal conductivity perpendicular to the graphene planes, and will not take advantage of the high basal plane thermal conductivity of graphite. Thus further development of the processing technology is required in order to reduce the lateral size of the GNPs without reducing the aspect ratio and compromising the bulk thermal conductivity of GNP filled greases.
The researchers presented their work in the Journal of Physics: Condensed Matter.
About the author
The work was performed at the Center for Nanoscale Science and Engineering and at the Departments of Chemistry and Chemical and Environmental Engineering of the University of California, Riverside. It was supported by DOD/DARPA/DMEA under the DMEA awards #H94003-08-2-0803 and #H94003-09-2-0904. Dr Xiaobo Sun and Dr Ramesh Palanisamy are postdoctoral fellows, Dr Elena Bekyarova and Dr Mikhail Itkis are staff scientists in Research Group of Robert Haddon. Research in the group of Robert Haddon focuses on the chemistry, material science, physics and applications of graphene, carbon nanotubes and organic molecular conductors.