Thermal Conductivity of Single-Walled Carbon Nanotube/PMMA Nanocomposites
, Fangming Du
, Stijn Brand
, John E. Fischer
, Karen I. Winey
Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA, USA.
Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA, USA.
Due to their exceptional thermal properties, single-wall carbon nanotubes (SWNT) are
considered as very promising filler materials for improving the thermal conductivity of
conventional polymers. We carefully investigated the thermal conductivity of SWNT/PMMA
nanocomposites with SWNT loading in the range up to10 wt% using the comparative technique.
The samples were prepared by coagulation method. We demonstrated moderate improvement in
the composites' thermal conductivity of about 250% at 10wt%. The experimental results were
analyzed using the versatile Nielsen model, which takes into account many important factors,
like the fillers aspect ratio and maximum packing fraction. The aspect ratio of SWNT material
used to prepare our composites was determined by AFM and careful image analysis in order to
use it as an input parameter in the Nielsen model. We obtained good agreement between our
experimental results and the predictions of the Nielsen model. Based on our analysis we
concluded that higher aspect ratio of filler material was needed to achieve better improvement in
the composites thermal conductivities. One should also take steps in order to improve the
thermal contact between the SWNT network and the matrix material.
The exceptional thermal and mechanical properties of single wall carbon nanotubes
(SWNT) make them a promising filler material for polymer composites. According to theoretical
calculations  the thermal conductivity of a (10, 10) SWNT is 6000 W/mK which is higher
than that of diamond. In addition, due to the very large aspect ratio of nanotubes (of the order of
2000 ) the percolation threshold for nanotube composites can be as low as 1% by volume.
Based on this, theoretical models predict that an addition of even a low volume fraction of
SWNTs would result in significant increase of a composite’s thermal conductivity. However,
experimental values of thermal conductivity for polymer-SWNT composites are generally lower
than those predicted by theory [2, 3, 4, 5]. Several studies [6,7] have suggested that a large
interfacial thermal resistance at the nanotube-polymer interface and between the nanotubes
themselves limits the thermal conductivity. An AFM study  has shown that the large aspect
ratio of nanotubes is not preserved during the processing of nanotubes for composites.
Experimental investigations of heat transport in these systems are still scarce, especially those